Why are skin moles (pigmented spots) circular in shape?

I have never seen a rectangular or triangular shaped mole. Is there any reason for why moles are roughly circular in shape?

Note: I am not stating that moles are in general circular in shape because there are no statistical studies to conclusively state so. This answer is mostly about default circular shape of cell colonies.

Moles (melanocytic naevi) are not strictly circular but generally have have a rough circular shape. Moles can have irregular shapes too and you can easily check that by a simple google image search.

The exact causes and mechanisms of mole formation are not known but the somewhat circular shape can be explained by a simple spatiotemporal model of growth.

Moles are formed because of pigmented cells called melanocytes (which contain the dark pigment melanin). A mole would grow when a very small population of these pigmented cells divide and expand. In a 2D surface, cells would continue to divide and expand along both the axis at an equal rate, if there are no specific constraints. Since the expansion is same along both the axes, you get a roughly circular shape. For similar reasons, bacterial colonies (on petri plates) are also more or less circular. Note that there are stochastic factors that would contribute to irregularity.

Triangles and rectangles are very specific geometries. There need to be some constraints that would limit the cell growth to adopt these geometries. So the default shape would be mostly circular.

Short answer
Naevi do not have to be circular in shape. In fact, they come in a wide variety of shapes and colors.

A beauty spot, or mole is called a naevus. Naevi (plural) are formed by the growth of the pigment cells in the skin, the melanocytes .

There are various types of naevi:

  • Congenital naevi are present from birth and occur in about one in 100 people. They may be more likely to develop into melanoma (cancer) than nevi appearing after birth (WebMD).
  • Acquired naevi develop later in life (Dermatology Net NZ);
  • Dysplastic naevi are typically larger than average and more irregular in shape. They tend to have uneven color with dark brown centers and lighter, uneven edges. These nevi are more likely to become melanomas (malignant skin cancer) (WebMD).
  • Dysplastic naevi may turn into melanomas (NIH), but melanomas are outside the scope of this question.

Now let's turn to your question - not all naevi are circular. Below I have illustrated just a mere tiny handful of the wide gamut of shapes found among different types of naevi. In fact, naevi come in a wide variety of shapes and colors (source: Dermatology Net NZ):

Small congenital naevus ; medium congenital naevus ; and hairy congenital naevus

Café au lait macule ; Speckled lentiginous naevus ; and Naevus of Ota

Reticular naevus ; Junctional naevus ; and Starburst naevus

In fact, naevi occur in more extreme forms too:

source: No Hands but Ours

- Cichorek, Postepy Dermatol Alergol (2013); 30(1): 30-41

Why Do People Get Moles on Their Skin?

The National Cancer Institute (NCI) reports that most people have at least 10 moles, and some persons have as many as 40. Moles are usually circular or oval in shape and may be either flush with the skin or raised above the surrounding skin layers. Most moles develop during the first 20 years of life, but some may not appear until later in life, according to the American Academy of Dermatology (AAD). New mole creation typically occurs until about the age of 40.

Naevi (moles)

Naevi, the technical term for moles, are commonly raised or flat spots that occur on the skin genetically and as a result of sun exposure. They are formed when melanocyte cells (the cells that give our skin pigment) grow in a group rather than individually. Most moles are benign, but they can also develop into skin cancer.

Harmless moles will have:

  • neat edges,
  • a smooth or dome-like shape
  • a re around ¼ inch (6 mm) in diameter
  • and stay the same shape, size or color over time.

Cancerous moles have a few common warning signs. Look for these indicators that your mole may be cancerous:

  • A change in size (getting larger)
  • A change in shape (especially with irregular edges
  • A change in color (especially getting darker or exhibiting multiple shades
  • A loss of symmetry (common moles will be perfectly round or oval and are usually symmetrical
  • Itchiness, pain or bleeding (maybe even forming a scab
  • Crustines
  • Inflammatio
  • Exhibiting three different shades of brown or blac
  • A change in elevation (thickening or raising of a flat mole)

Acne is an extremely common skin condition that can range from mild to severe. The condition usually presents itself as skin bumps that often become red or swollen. Acne can also take the form of whiteheads, blackheads, papules, pustules, cysts, and nodules. Severe acne can leave scars if not treated in time. There are many acne treatments available ranging from topical products to prescription medication, a doctor or dermatologist should be consulted to find the appropriate treatment.


Hives are a rash of red bumps that occur suddenly on the skin usually as a result of an allergen. They usually last for hours or a few days before subsiding. Hives are very common and can show up anywhere on the body, even moving around, disappearing and reappearing over a matter of hours. Treatments are directed at the symptoms until the hives can clear up on their own. Usually, antihistamines are recommended.


Eczema, also known as atopic dermatitis, is a skin condition that causes red, itchy and dry skin as a result of inflammation. Sometimes white patches or spots can form within a red rash. This condition is typically found in children but can continue into adulthood. Eczema symptoms include dry, scaly, thickened skin that is almost always itchy. Especially among darker-skinned people, eczema can cause skin discoloration, making the affected area lighter or darker than the surrounding skin.

The cause of eczema is unknown but it is thought to be linked to allergies and asthma and is suspected to be an overactive immune response to an irritant. While there is no cure for the condition, symptoms can be managed. For many people, eczema will even go away over time. Doctors can prescribe topical corticosteroid creams and ointments, oral medications and light therapy to help ease symptoms.


Rosacea is a chronic skin condition that causes tiny red pimples and redness of the skin. It typically only occurs on the face and it is common for small blood vessels to appear on the surface of the skin. Rosacea often starts with a tendency to blush or flush easily. The condition can also make skin thick and cause acne-like breakouts. It is treated with topical ointments, antibiotics, lasers, and other light treatments.


Psoriasis is a chronic skin disease that causes red, scaly and itchy plaques to form on the skin. It is caused by skin cells multiplying faster than normal. Psoriasis can also take the form of small red spots, pus-filled bumps, as red patches that feel sore or as skin that becomes bright red and appears burnt. It often occurs on the knees, elbow, and scalp, and, although it is incurable, it usually responds well to treatment. Treatments include topical creams, medicines, ultraviolet light treatments and more.


Impetigo is a contagious bacterial infection of the skin. It is more common in children than adults and is caused by the Staphylococcus (staph) and Streptococcus bacteria. Impetigo presents itself as small red spots that morph to blisters which can eventually break open and ooze fluid. Sores may also be crusty and can range in size from the size of a freckle to larger than a coin. Impetigo is usually treated with antibiotics, in the form of pills or an ointment.


Warts are small benign tumors that are caused by one of over 100 types of human papillomaviruses (HPV). Warts are often contagious and can be spread through physical contact. There are many different types of warts that can occur on the body.

Common warts usually grow on fingers, nails and the back of hands. They usually appear as domed, rough bumps. Contact a doctor to identify which type of wart you have and to advise a course of treatment. Warts will often disappear on their own but they can also be treated by a dermatologist or doctor.

The most common treatment is cryotherapy, or the freezing off of warts. Excision, electrosurgery, and curettage are other treatment options.

Skin cancer

There are many different kinds of skin cancer, separated into non-melanoma and melanoma skin cancers. Basal cell carcinoma is the most common form of skin cancer and the least dangerous, usually appearing as a small lump that gets bigger over time.

Squamous cell carcinoma is less common but faster spreading. It usually presents itself as rough, scaly plaques that can bleed easily. Melanoma is the rarest and most dangerous form of skin cancer, typically developing from a new mole on the body. Skin cancer treatments range widely based on the type, severity, and health of the patient. Any suspicious marks should be checked out by a doctor or dermatologist early.

Pigmentation: Abnormal Pigmentation

Birthmarks and other skin pigmentation (coloration) disorders affect many people. Some of the most common problems are listed below. If you think you have one of these pigmentation abnormalities, be sure to see a physician or dermatologist to receive an official diagnosis.


As might be expected, these abnormal skin colorations will appear at birth or just a few weeks after birth. While most birthmarks are non-cancerous, certain birthmarks, described below, can pose health risks.

Pigmented birthmarks

This birthmark is marked by bluish or grayish discoloration of the face and sometimes the white part of the eye (sclera). The discoloration is caused by increased amounts of the pigment (melanin) and the cells that produce this pigment (melanocytes) in and around the eyes. Patients with this type of birthmark are at a higher risk of developing a melanoma cancer of their eye or central nervous system. In addition, they may develop glaucoma (increased pressures in their eyes). For this reason, they should have regular examinations by a neurologist as well as an ophthalmologist. Potential treatments for this skin discoloration include topical (applied on the skin) bleaching agents, such as hydroquinone, and laser treatments.

These birthmarks appear bruised or bluish in color and usually develop on the back or buttocks of babies. This discoloration usually disappears by age 4 and does not need to be treated.

These are light brown-to-dark brown flat spots with smooth or irregular borders. About 10% of the general population has 1 or 2 of these spots, and do not have another disorder that is related to it. However, 6 or more of these spots that are greater than 0.5 cm in diameter can be associated with the genetic disorder neurofibromatosis. These birthmarks may be treated with a laser for cosmetic purposes.

These spots may be flesh-colored to light-to-dark brown. They may be flat or raised. Although most moles are benign (non-cancerous) and will not cause any problems, some may change and become a skin cancer called a melanoma. For this reason, moles should be watched for bleeding, pain, itch, color, shape, symmetry, even borders, and size changes.

  • A way to check these moles is ABCDE:
    • A for asymmetry. If you divide your mole in half, both sides should look the same.
    • B for border. The border of your mole should be even.
    • C for color. Your mole should be one color. Your mole should not have a variety of colors, especially colors like red or blue.
    • D for diameter. Moles less than 0.6 cm in diameter are usually benign. If your mole increases in size, especially if it is greater than 0.6 cm, you should have it checked.
    • E for evolving or elevation. If your mole was flat but is now elevated (raised), or if you notice bleeding, crusting, pain, or itching, this should be checked out.

    If any of these features change, you should have your moles examined. If you have a personal or family history of melanoma, you should have a regular examination of your moles by a dermatologist.

    Vascular birthmarks (from blood vessels)

    Macular stains appear anywhere on the body as mild red marks, but they are not elevated. They are the most common type of vascular birthmark. They can come in two forms: “angel kisses,” which may appear on the forehead and eyelids and usually disappear after age two or “stork bites,” which will appear on the back of the neck and can last into the adult years. Because these marks are often mild and always harmless, they do not need to be treated.

    Hemangiomas are growths that are made up of many tiny blood vessels bunched together. Some hemangiomas are more serious. They are more common in females and premature babies. This birthmark is usually just a small mark on the face, trunk, or extremities (arms and legs). However, in some children, hemangiomas can be large and grow rapidly through the first year of life.

    There are 2 types of hemangiomas: strawberry (or superficial), which are slightly raised and can appear anywhere on the body or cavernous (deep), which are deeper birthmarks marked by a bluish color. Fortunately, most hemangiomas will go away on their own: 50% get better by age 5, 70% by age 7, and 90% by age 9.

    If the hemangioma is small and not causing any problems, it can be watched to see if it gets better. Reasons to treat a hemangioma include problems with functions (such as sight, eating, hearing, or defecation), ulceration, bleeding, or pain.

    If necessary, hemangiomas can be treated in different ways, each of which carries its own risks. Corticosteroid medication can be injected or taken orally (by mouth). Risks of corticosteroid medication include high blood pressure, high blood sugar, poor growth, or cataracts. Certain hemangiomas can also be treated with lasers to stop them from growing, and heal them. Rare risks associated with laser treatment include ulceration and scarring. In addition, both topical and oral beta blocker medication has been used to treat hemangiomas, but these medications also carry their own risks that should be carefully discussed with your dermatologist. In rare cases, a hemangioma can be removed with surgery.

    A port wine stain appears as a flat pink, red, or purple mark on the face, trunk, arms, or legs, and lasts a lifetime. Port wine stains are caused by abnormal development of blood vessels (capillaries). Over time, the port wine stain may become raised and thickened. Port wine stains on eyelids are thought to pose an increased risk of glaucoma. Physicians have tried many ways to treat port wine stains, including radiation, tattooing, freezing, dermabrasion, or sclerotherapy. Laser therapy is currently the treatment of choice, as it is the only method that destroys capillaries in the skin without causing damage to the rest of the skin. Port wine stains may be seen in certain medical disorders, such as Sturge-Weber Syndrome, whose symptoms include port wine stains on the face, vision problems, convulsions, mental retardation, and perhaps even paralysis and Klippel-Trenaunay Syndrome, in which a limb has port wine stains, varicose veins, and/or too much bone and soft tissue growth. Both of these syndromes are very rare.

    Skin pigmentation disorders

    Albinism, an inherited disorder, is caused by the absence of the pigment melanin, and results in no pigmentation in the skin, hair, or eyes. Albinos have an abnormal gene that restricts the production of melanin. There is no cure for albinism. People who have this disorder should use a sunscreen at all times because they are much more likely to get sun damage and skin cancer. Albinism can occur in any race, but is most common in Caucasians. In addition, almost all patients with albinism have problems with their eyes, such as decreased vision or abnormal eye movement, and should be seen by an ophthalmologist.

    Melasma (also known as chloasma) is marked by tan or brown patches that may appear on the forehead, cheeks, upper lip, nose, and chin. Although this condition is often called the "pregnancy mask," men can also develop it. It may also occur in women who are taking birth control pills or postmenopausal estrogen. Melasma may go away after pregnancy, but if it remains, it can be treated with certain prescription creams and some over-the-counter skin care products. In addition, lasers that target pigment can be helpful. Remember to consult your dermatologist for a proper diagnosis of this condition before you choose to treat it yourself. If you have melasma, use a sunscreen at all times because sunlight will make the condition worse.

    • Pigmentation alteration (change) as a result of skin damage (post-inflammatory hyper- or hypopigmentation)

    If you have had a skin infection, blisters, burns, or other trauma to your skin, you may have a decrease or increase of pigmentation in the affected area. This type of alteration is usually not permanent, but may take up to several months to fade or get better. Cosmetics can be used to cover the area. In the case of hyperpigmentation (dark spots), prescription or over-the-counter lightening creams may help decrease the amount of time for the areas to fade. You should also wear sunscreen, as sunlight can prolong the darkness of the areas.

    Vitiligo is a condition where the body’s immune system attacks pigment cells (melanocytes), causing pigment loss. Other immune system diseases associated with vitiligo include diabetes, pernicious anemia, thyroid disease, and Addison’s disease. Vitiligo causes smooth, white skin patches, usually around the mouth and eyes, or on the back of the hands. In some people, these patches can appear all over the body. There is no cure for vitiligo, but there are several treatments, including: topical steroid preparations topical immunomodulators topical vitamin D analogs dyes or psoralens (light-sensitive drugs) used in combination with ultraviolet A (UVA) light treatment and, the Excimer laser, which delivers targeted ultraviolet B (UVB) light. All treatments may take 6 or more months to be effective.


    Brown skin spots that arise from prolonged exposure to the sun, hormonal changes, or post-inflammatory changes do not need treatment especially if they are not accompanied by other symptoms. However, many people seek treatment for cosmetic reasons to improve their appearance such as the use of Olay Correcting Spot Treatment.

    In cases of skin cancer, the underlying disease must be treated to protect the individual’s health. Brown skin spots caused by excessive sun exposure, aging,or post-inflammatory hyperpigmentation may be treated using over-the-counter creams and lotions to lighten the spots. Cosmetic products may also be used to hide them, including skin-bleaching products that may contain tretinoin, hydroquinone, or kojic acid. Prescription strength skin lightening products that contain retinoic acid (a vitamin A derivative) and steroids may also be recommended by dermatologists.

    Exfoliating products, which contain glycolic acid, papaya extract, or salicylic acid, are also available as OTC treatments. Skin brightening compounds and bleaching lotions withhydroquinone, licorice extract, and bearberry also work with fruit acids to lighten dark spots, including the product NIA 24 .

    Other treatment methods to reduce brown spots and improve skin appearance include phototherapy, microdermabrasion, chemical peeling, and laser treatment.

    Skin Spots on the Face

    Most causes of spots on face are harmless. They can be a variety of colors including white, red, black or brown. Common causes include cumulative sun exposure, acne, and skin tags.

    Keratoacanthoma (hyperkeratosis) is a lesion that grows rapidly, usually on areas exposed to the sun. Lesions are shaped like a dome and are usually red to tan/brown. Treatment is with surgical. removal. Can also be treated with topicals. It can destroy skin tissue in areas where the tumor grows. The condition is considered to be related to squamous cell carcinoma, although a biopsy is needed to determine if the condition is cancerous in nature.

    Any face lesions should be differentiated from cancerous conditions such as basal cell carcinoma, the most common form of cancer in people. The condition primarily occurs in men (but can occur in women) over age 40. It is very rare in people that have black or brown skin. Skin tumors are slow growing and can cause bleeding.

    Treatment involves surgical removal, electrodesiccation, and cryosurgery.

    No, these spots do not go away on their own. So, whether you have a mole, wart, or skin tag, a board-certified dermatologist can give you the most accurate identification and help you decide if the growth should be removed.

    If you have a problematic spot on your skin, contact us to schedule a consultation and discuss your wart or mole removal options.

    Dr. R. Todd Plott is a board-certified dermatologist in Coppell, Keller, and Saginaw, TX. His specialization and professional interests include treating patients suffering with acne, identifying and solving complex skin conditions such as psoriasis, rosacea, atopic dermatitis, and identifying and treating all types of skin cancers. In his spare time, Dr. Plott enjoys cycling, traveling with his wife, and spending time with his children and new grandson.

    White Spots On Skin – Causes, Treatment, Symptoms

    A white spot on the skin is a common problem and occurs due to lack of skin pigmentation substance called melanin. It can occur in the form of dark spots, white spots or other colored spots on the skin. Similarly it may occur either in the shape of circular spots or dark patches anywhere in the body. It is largely found in the neck, upper back, shoulders, forearms and the shins. These spots do not cause any pain or discomfort but has gained importance for cosmetic purpose.

    White spots are common on men and women and people with fair complexion and those living in hot climatic conditions are prone to get more number of white spots than others.

    One of the main causes for getting white spots on skin is vitiligo. Melanocytes present in the skin produces melanin, a skin pigment responsible for giving coloration to the skin. If melanin is secreted in less quantity or totally absent it can result in formation of white spots. It can happen due to autoimmune disorder where body’s own immune system destroys healthy cells of melanin causing discoloration.

    Vitiligo is commonly present in 3 million Americans which count for 2-3 % of total population of America. White spots occur during the age of 25-35 years affecting both sexes equally.

    Who Are At Risk?

    Those who are predisposed to vitiligo or with family history are more prone to get white spots than others. People with Hashimoto’s thyroiditis an autoimmune disorder can get white spots in middle age. Men with grey hair during early ages are also under risk of having white spots quickly.

    Read more on Brown Spots On Face

    Exposed parts of the body like hands, legs, shoulders and back portion are quickly affected with white spots. Vitiligo will not affect the person totally. It leaves a gap known as period of stability during which the process of discoloration stops. This is followed by repeated whitish spots on the skin. It can affect the folds of the skin like armpits or areas in which there is skin injury. For some people it can occur on the areas where skin is injured or moles have developed. In rare cases it may develop on eyelids and on hair.

    Your doctor can easily identify the white spots by thorough physical examination.

    Pictures of White Spots on Skin :

    Images, Pics, Pictures and Photos of White Spots on Skin

    No treatment is required for white spots on the skin since they are benign (harmless) and does not cause pain or irritation. However many people want to remove it for cosmetic reasons. It is difficult to treat vitiligo but treatment can be given for improving the appearance and skin color. Your doctor will induce pigmentation process for getting back the normal skin color on the affected areas. He may also prescribe corticosteroid or give phototherapy for removing the white spots.

    There are several types of white spots like Tinea versicolor, idiopathic guttate hypermelanosis and pityriasis Alba. Skin grafting is done for removing white spots, in which normal skin is replaced by removing it from other body parts and fixing it on affected areas. Antifungal drugs like clotrimazole and terbinafine are given for treating Tinea versicolor.

    Idiopathic guttate are commonly seen on fair complexioned women and here white spots of size 2-5 mm in diameter can develop as scaly patches. It is believed to run on families passing the genetic factors from one generation to the other. Pityriasis Alba affects young children and is characterized in the form of dry scaly white spots on the face.

    Your doctor will identify the real cause for such discoloration before starting the treatment. In case of deficiency or malnutrition he would prescribe supplementary vitamin capsules for producing natural melanin to remove discoloration. If the white spots are formed due to lack of amino acid by name tyrosine then you need to take drugs to produce that amino acid so that discoloration disappears in due course.

    Why do red moles appear on my skin?

    The appearance of red moles on the skin, also called angiomas, can have several origins:

    • Overexposure to the sun
    • Bad nutrition
    • Low water consumption
    • Aging
    • Excess toxins in the liver, blood, intestines, and pancreas
    • Excessively white and delicate skin

    It is that any of these causes can promote the abnormal growth of tiny blood vessels. Its measurement ranges between 1 and 4 millimeters, with a circular and uniform shape although in relief, and in some cases it can also appear on the heels, armpits and genital areas.

    Do not be alarmed by the presence of a few red moles on the skin, as long as they maintain their size, quantity and color. That is, as long as they do not change their appearance, especially in size or texture (they become rough), shape and color and do not exceed a certain amount (three to five in a specific area).

    If it is a red mole that appeared out of nowhere but changes its appearance over time, becoming dark, deformed and larger, then it is necessary and mandatory to go to the dermatologist to perform the recommended tests.

    If you are only in the presence of red moles, it is best to pay attention to your diet, habits and lifestyle, and skin care in general.

    Can you spot the cancerous mole?

    25% of melanomas arise from an existing mole. That means that the majority of melanomas are new moles – so they should be easy to spot, right?

    Unfortunately, new moles are often overlooked, and ones that you’ve had your whole life can change without you realizing it. And change is a major indicator of skin cancer.

    A melanoma is a cancerous tumor that looks like a mole. It is the number one death-causing skin cancer, even though it only makes up 5% of skin cancer cases. The reason it’s so dangerous is because melanoma cells can easily spread through your body. Once they reach the lymph nodes, they can spread to other vital organs such as the lungs.

    Moles are extremely common. Some people are born with them and others can develop moles later in life due to hormonal changes like puberty or pregnancy. They form in the epidermis – the top layer of the skin. This is where the melanocytes produce melanin, causing skin pigmentation. Melanin production increases when you spend more time in the sun, and when melanocytes group together, they form a mole.

    The ABCDE Method

    The American Academy of Dermatology recommends the ABCDE method for monitoring your moles: (See images below for examples.)

    • Asymmetric shape – non-cancerous moles are symmetrical
    • Border irregularity – melanomas have notches or blurred edges while moles are more sharply defined
    • Color variability – the color is distributed unevenly in cancerous moles
    • Diameter – moles are typically smaller than ¼ inch
    • Evolution – changes in size, shape, and color can indicate a melanoma
    • Extra features – if a new mole is bleeding or itching, it could be cancerous

    If you notice any of these features, consult your doctor for a full skin check. The doctor may have the mole removed and if cancerous, and will also check to see if the cancer has spread. If it has spread, chemotherapy and radiation therapy can kill cancer cells. It’s much easier to treat if the melanoma is detected early!

    People with naturally large moles have a higher risk for developing skin cancer. People with a history of frequent sunburns also have a much higher risk. Those with fair skin, blonde or red hair, and a family history of melanoma are also more susceptible to skin cancer.

    Early diagnosis is crucial for treating melanomas. Even if you see the doctor for regular check-ups, it’s important to inspect your freckles and moles every few months to see if any of them have changed shape or grown.

    If you thought this we easy, try our new quiz here

    Moles up close

    This is a melanoma. The edges have notches, the color is inconsistent, and it is asymmetrical.

    This mole is tricky it is actually benign, though it may be confused for a cancerous mole. The edges are slightly blurred and the color is not perfectly consistent. This is called a dysplastic mole because it appears different from other moles on the body. People with multiple dysplastic moles may have an increased risk of developing melanomas even though the moles themselves are not cancerous. Therefore, it’s a good idea to have the dermatologist check it out.

    Get peace of mind and do not wait!

    We had a recent user that decided not to pay for a dermatologist to look at a picture of his mole, our team of dermatologists think it looks like a melanoma. What do you think? Read the full story here