Uncommon Skin Cancers: Hidden Signs and Unexpected Places To Check

When it comes to skin cancer prevention, most people often focus on moles. However, there are many uncommon forms of skin cancer that manifest as harmless bumps, rashes, scars, infections, or wounds that simply refuse to heal. Additionally, skin cancer can develop in easy-to-miss areas, including the scalp, eyelids, lips, nails, soles of the feet, and even intimate areas where the sun doesn’t shine. Since these warning signs are less commonly recognized, or occur in areas that many people do not associate with skin cancer, they may be mistaken for minor skin issues rather than something that needs evaluation.

In this blog post, we’ll discuss uncommon skin cancers in depth. The goal is awareness, not alarm. Knowing that skin cancer can appear in unexpected ways can help patients recognize when a spot deserves a closer look.

Rare or Less Common Skin Cancers

Basal cell carcinoma, squamous cell carcinoma, and melanoma are the most commonly discussed skin cancers. However, there are several rare or less common types patients should be aware of.

• Merkel cell carcinoma: A rare, aggressive skin cancer that may appear as a fast-growing, firm, painless bump. It can be red, pink, purple, or skin-colored and often appears on sun-exposed areas.
• Sebaceous carcinoma: A cancer of the oil glands that can develop near the eyelid and may be mistaken for a recurring stye or chalazion.
• Acral lentiginous melanoma: A melanoma subtype that can appear on the palms, soles, or under the nails. It can occur in areas not typically associated with sun exposure.
• Mucosal melanoma: A rare form of melanoma that develops in mucosal tissue, such as the mouth, nose, genital area, or anal region.
• Kaposi sarcoma: A cancer that may appear as red, purple, or brown lesions, more often in patients with weakened immune systems.
• Dermatofibrosarcoma Protuberans: This rare cancer often appears as slow-growing, painless, firm skin-colored or red-brown plaque on the skin. It can become elevated and have protruding nodules almost like a keloid like scar on the skin.
• Cutaneous lymphoma: A type of lymphoma that affects the skin and may mimic eczema, psoriasis, or a persistent rash.

Uncommon Places Skin Cancer Can Occur

Did you know that skin cancer can develop almost anywhere on the body? While sun-exposed areas are still important, a more complete skin check should include hidden and less obvious locations including:

Scalp and Hairline

The scalp is easy to miss, especially when hair covers the skin. Skin cancers can hide along the part line, temples, crown, and hairline. Patients with thinning hair, a history of sun exposure, or outdoor lifestyles should be especially careful.

To make checking the scalp easier, consider asking your partner, hairstylist, or dermatologist to look for new, crusted, bleeding, or non-healing spots.

Ears and Behind the Ears

The ears receive significant sun exposure but are often missed when applying sunscreen. Skin cancer can occur on the rim of the ear, inside the outer ear, behind the ear, or in the crease where the ear meets the scalp.

Watch for rough patches, tender spots, non-healing sores, or areas that repeatedly crust or bleed.

Eyelids and Around the Eyes

The eyelids are delicate and often overlooked. A persistent bump, thickened eyelid area, sore that does not heal, or a “stye” that keeps coming back should be evaluated.

This is especially important because sebaceous carcinoma can sometimes appear near the eye and mimic more common eyelid conditions. Any recurring or unusual eyelid growth deserves medical attention.

Lips and Inside the Mouth

The lips are vulnerable to sun damage, especially the lower lip. Skin cancer may appear as a persistent rough patch, bleeding area, sore, crusted spot, or color change.

Although rare, melanoma can also develop in mucosal areas, including inside the mouth. Persistent dark spots, sores, or bleeding areas in the mouth should not be ignored. These can be discussed with your dentist or dermatologist

Under the Nails

Nail changes are one of the most important hidden warning signs. Skin cancer under or around the nail may look like a dark streak, a pigment band, a spot that resembles a bruise, nail splitting, nail lifting, or a non-healing sore near the nail.

A normal bruise under the nail should resolve or heal overtime. If a dark streak or spot does not move with nail growth, widens, changes, or affects the surrounding skin, it should be checked.

Palms, Soles, Toes, and Between Toes

Many patients assume skin cancer only appears where the sun hits. However, certain melanomas can occur on the palms, soles, toes, or between the toes.

Because these areas are not always associated with sun exposure, patients may mistake concerning spots for calluses, bruises, warts, blisters, or minor injuries. Any new, changing, bleeding, or persistent spot on the feet or hands should be evaluated.

Genital and Anal Areas

Skin cancer can also occur in genital or anal areas, although this is less common. Since these areas are private, patients may delay getting evaluated due to embarrassment or the assumption that the lesion is a rash, wart, irritation, or infection.

Any persistent sore, bleeding area, lump, wart-like growth, changing pigmented spot, or lesion that does not improve should be discussed with a medical provider, such as a GYN, urologist or dermatologist.

Old Scars, Burns, or Chronic Wounds

Some skin cancers, especially squamous cell carcinoma, can develop in chronically injured, inflamed, or scarred skin. This may include old burn scars, long-standing wounds, radiation sites, or areas of chronic irritation.

A scar or wound that changes, thickens, bleeds, becomes painful, or fails to heal deserves evaluation.

Warning Signs That Deserve Attention

Skin cancer can look different from person to person, but certain warning signs should not be ignored. Schedule an exam if you notice:

• Non-healing sores or wounds
• Bleeding, crusting, or recurring spots
• Firm or fast-growing bumps
• Pimple-like growths that do not clear
• Scar-like patches without a known injury
• Dark streaks or pigment changes under the nail
• Rough or scaly patches that do not improve
• Lesions in hidden or intimate areas
• Spots that look noticeably different from others
• Rashes that do not respond to treatment

Persistence is the most alarming factor: if something is not healing, keeps coming back, or continues to change in appearance, it should be checked.

Why Skin Cancer Can Occur in Places Without Much Sun

UV exposure is a major driver of many skin cancers, but not every skin cancer is purely sun-related. Some cancers may be influenced by genetics, immune suppression, chronic inflammation, previous injury, HPV, or other factors.

That is why skin cancer can occur on areas like the soles of the feet, under the nails, inside the mouth, or in genital skin. Sun protection is still essential, but it should not be the only way patients think about skin cancer prevention and detection.

A complete skin awareness routine includes both sun-exposed and hidden areas.

How to Do a Better Self-Check

Self-checks (monthly skin checks you perform at home) are most useful when they are thorough and consistent. Instead of only looking at obvious moles, patients should occasionally do a head-to-toe review that includes areas they do not commonly examine on a daily basis including:

• scalp and part line
• ears and behind the ears
• eyelids and lips
• under the breasts and skin folds
• palms and backs of hands
• fingernails and toenails
• soles and between toes
• genital or anal area if symptoms or changing spots are present
• old scars, burns, and chronic wounds

Use a mirror for hard-to-see areas or ask a partner to help. Photos can also be useful for tracking whether a spot is changing over time.

When to See a Dermatologist

The best way to protect yourself from uncommon skin cancers is to visit your dermatologist annually for a professional skin check. A dermatologist can examine the skin more thoroughly, use tools such as dermoscopy, and biopsy suspicious lesions when needed.

Beyond annual checks, patients should schedule a dermatology exam if they notice any new, changing, painful, bleeding, crusting, or non-healing lesion. This is especially important when the spot is in a hidden area, under a nail, near the eye, on the lips, or in a scar.

Adam Mamelak, MD is an American and Canadian Board Certified Dermatologist and an American Board Certified, Fellowship-Trained Mohs Micrographic Surgeon at Westlake Dermatology. Dr. Mamelak obtained his Bachelor degree and graduated in the top 5% of the Faculty of Science from McGill University, and was a gold medalist (the highest honor obtainable) in his medical class at Queen’s University. He completed his Dermatology residency training at The Johns Hopkins University, where he also completed a research fellowship in Molecular Immunology. Dr. Mamelak completed fellowship training in Mohs Surgery/Procedural Dermatology at the Methodist Hospital in Houston.

Disclaimer: The contents of the Westlake Dermatology website, including text, graphics, and images, are for informational purposes only and are not intended to substitute for direct medical advice from your physician or other qualified professional.