Skin rashes are a common condition. They usually stem from something harmless, like a reaction to heat, medication, a plant like poison ivy, or a new detergent you’ve touched.

Rashes can show up on any part of your body, from your head to your feet. They can even hide in the cracks and crevices of your skin. Sometimes they itch, crust, or bleed.

Occasionally, bumps or redness on your skin can be a sign of cancer.

For example, if you notice an itchy mole on your chest that seems to be changing shape, there’s a chance you’re dealing with skin cancer.

Because cancer can be very serious — even life threatening — it’s important to know the difference between a rash caused by irritation and one caused by skin cancer.

This is why it’s important to talk with a dermatologist about any rash or growth that’s new, changing, or not going away.

While skin cancers are often asymptomatic, meaning they don’t show symptoms, they can be itchy.

For instance, basal cell skin cancer can appear as a raised reddish patch that itches, and melanoma can take the form of itchy dark spots or moles.

Talk with your doctor about any itchy, crusty, scabbed, or bleeding sore that’s not healing.

The most common symptom of skin cancer is a change in your skin, such as a:

  • new growth
  • sore that’s not healing
  • mole that’s changing color or shape

Melanoma is a less common but more dangerous form of skin cancer because it can spread easily if not treated. One of the best ways to get a handle on its symptoms is to think of “A-B-C-D-E.”

  • “A” for asymmetrical. Do you have a mole or spot that seems to be shaped oddly or have two sides that look different?
  • “B” for border. Is the border of your mole or spot jagged?
  • “C” for color. Is the color of your mole or spot uneven or different?
  • “D” for diameter. Is your mole or spot bigger than the size of a pencil eraser?
  • “E” for evolving. Have you noticed your mole or spot changing in an obvious way?

If any of these apply to a mark on your skin, it’s important to talk with a dermatologist as soon as possible.

Mycosis fungoides

Mycosis fungoides is the most common form of cutaneous T cell lymphoma, a type of blood cancer that involves infection-fighting white blood cells called T cells.

When these cells turn cancerous, they form a red, scaly rash on the skin. The rash can change over time, and it may:

  • itch
  • peel
  • hurt

Mycosis fungoides often shows up as an eczema-like rash in areas that typically get little sun exposure.

Actinic keratosis

Actinic keratoses are crusty or scaly pink, red, or discolored bumps that appear on areas of sun-exposed skin, including the:

  • face
  • scalp
  • shoulders
  • neck
  • backs of your arms and hands

If you have several of them together, they can resemble a rash.

They’re caused by damage from the sun’s ultraviolet (UV) radiation. If you don’t get actinic keratosis treated, it can turn into skin cancer. Treatments include:

  • cryosurgery (freezing them off)
  • laser surgery
  • scraping off the bumps

Actinic cheilitis

Actinic cheilitis looks like scaly bumps and sores on your lower lip. Your lip might also be swollen and red.

It’s caused by long-term sun exposure, which is why it often affects people with lighter skin who live in sunny climates or individuals who spend a lot of time working outside.

Actinic cheilitis can turn into squamous cell cancer if you don’t have the bumps removed.

Cutaneous horns

Just as the name suggests, cutaneous horns are hard growths on the skin that look like an animal’s horns. They’re made from keratin, the protein that forms skin, hair, and nails.

The horns are concerning because about half the time they grow out of precancerous or cancerous skin sores. Larger, painful horns are more likely to be cancerous.

You’ll usually just have one cutaneous horn, but they can sometimes grow in clusters.

Moles (nevi)

Moles, also called nevi, are flat or raised areas of skin. They’re usually brown or black, but they can also be:

  • tan
  • pink
  • red
  • skin-colored

Moles are individual growths, but most adults have between 10 and 40 of them, and they can appear close together on the skin.

Moles are often benign, but in some cases, melanoma — the most serious type of skin cancer — can begin within a mole.

Seborrheic keratosis

These brown, white, or black bumpy growths form on parts of your body, like your:

  • stomach
  • chest
  • back
  • face
  • neck

They can be tiny or can measure more than an inch across. Although seborrheic keratosis sometimes looks like skin cancer, it’s actually harmless.

However, because these growths can get irritated when they rub against your clothes or jewelry, you may choose to have them removed.

Basal cell carcinoma

Basal cell carcinoma is a type of skin cancer that appears as red, pink, or shiny growths on the skin, but it can also appear as dark or gray-colored lesions, especially on individuals with darker skin tones.

Like other skin cancers, it’s caused by prolonged exposure to the sun.

While basal cell carcinoma rarely spreads, it can leave permanent scars on your skin if you don’t treat it.

Merkel cell carcinoma

This rare skin cancer looks like a reddish, purple, or blue-colored bump that grows quickly. It can look like:

  • a cyst
  • an insect bite
  • a sore
  • a pimple

You’ll often see it on your:

  • face
  • head
  • neck

It’s more common in people with lighter skin who have had lots of sun exposure, although the exact cause is still not known.

Basal cell nevus syndrome

This rare inherited condition, which is also known as Gorlin syndrome, increases your risk of developing basal cell cancer as well as other types of tumors.

The disease can cause clusters of basal cell carcinoma, especially on areas like your:

  • face
  • chest
  • back

A rash is less likely to be cancer if you’ve taken these steps to protect your skin:

  • Try to limit your time in direct sunlight during the hours when the sun’s UV rays are strongest, which are from 10 a.m. to 4 p.m.
  • If you do go outside, apply a broad-spectrum (UVA/UVB) SPF 30 or higher sunscreen to all exposed areas. Reapply after you swim or sweat, or every 2 hours.
  • In addition to sunscreen, you can wear sun-protective clothing. You can also wear a broad-brimmed hat and UV-protective sunglasses.
  • Try not to use tanning beds.

Check your own skin for any new or changing spots once a month. You may also contact your dermatologist for an annual whole-body check.

In addition to yearly appointments with your dermatologist, it’s a good idea to regularly check your skin for any moles or red patches that either seem to appear or change over time.

According to the American Cancer Society, you should consider making an appointment with your dermatologist if you notice a:

  • new, expanding bump or growth on your skin
  • sore that continues to bleed or doesn’t heal for several weeks
  • rough, red, or scaly patch that crusts over or bleeds
  • wart-like growth
  • mole that seems to be changing color or shape
  • mole with irregular borders

When it comes to rashes and spots of all kinds, talk with your doctor if you are unsure.

If you don’t already have a dermatologist, your general doctor may refer you to one if they believe you have a suspicious patch or mole on your skin.

During a dermatologist appointment, you will most likely be asked about:

  • your symptoms
  • whether you remember when the mark first appeared
  • whether you have a personal history, or any family history, of skin cancer.

After your dermatologist examines the area in question, they may decide to do a biopsy.

There are a few ways to go about performing a biopsy when it comes to the possibility of skin cancer, but in most cases, your dermatologist will use a local anesthetic to numb the area. Then they’ll take a tiny sample of that skin to look at under a microscope.

In very rare cases, your doctor may decide to order an MRI or CT scan of the area if they believe the cancer may have spread below the skin.

How can you tell if a rash is serious?

In many cases, a rash will go away on its own. However, if you notice any of the following symptoms along with a new rash, you should contact your doctor immediately:

  • The rash is all over your body.
  • You have a fever.
  • The rash appears suddenly and spreads quickly.
  • The rash becomes red, itches, and blisters.
  • The rash is painful.
  • The rash looks infected.

What does a cancerous rash look like?

Cancerous rashes, marks, and moles can vary in their appearance. If you notice a red, scaly patch on your skin that itches, cracks, or bleeds — and doesn’t seem to be healing — there is a chance it could be cancerous.

Talking with your doctor or a dermatologist is the best way to figure out if you’re dealing with a less serious rash or something that will need to be biopsied.

As a general reminder, if you notice a mark on your skin that’s changing shape or color, it’s important to get a medical opinion as soon as possible.

Are skin cancers itchy?

While many skin cancers may not have any symptoms, some can be itchy.

Basal cell skin cancer can appear as an itchy, reddish patch. Melanoma can also occasionally appear as dark spots or moles that itch. Mycosis fungoides, which is a form of T cell lymphoma, also presents as red, itchy spots on the skin.

Skin rashes are common, and many of them clear up on their own or with over-the-counter medication. However, a very small percentage of skin rashes may be a sign of skin cancer.

If you notice a suspicious mark on your skin that seems to be changing shape or color, you should talk with your doctor or dermatologist as soon as you can. With their help, you will be able to quickly get to the bottom of your issue and receive treatment.