The typical symptoms of Crohn’s disease stem from the gastrointestinal (GI) tract, causing issues like belly pain, diarrhea, and bloody stools. Yet up to 40 percent of people with Crohn’s disease have symptoms in other areas of their body, such as their skin.

Here are some of the most common skin conditions related to Crohn’s disease, and how doctors treat them.

Erythema nodosum causes red, painful bumps to erupt on the skin, usually on the shins, ankles, and sometimes the arms. It’s the most common skin manifestation of Crohn’s disease, affecting up to 15 percent of people with this condition.

Over time, the bumps slowly turn purple. Some people have a fever and joint pain with erythema nodosum. Following your Crohn’s disease treatment regimen should improve this skin symptom.

Large open sores on your legs and sometimes other areas of your body are a sign of pyoderma gangrenosum. This skin condition is rare overall, but it affects up to 5 percent of people with Crohn’s disease and ulcerative colitis.

Pyoderma gangrenosum usually starts with small red bumps that look like insect bites on the shins or ankles. The bumps grow larger and eventually combine into one big open sore.

Treatment involves medication that’s injected into the sore or rubbed on it. Keeping the wound covered with a clean dressing will help it heal and prevent infection.

Anal fissures are small tears in the skin lining the anus. People with Crohn’s disease sometimes develop these tears because of chronic inflammation in their intestines. Fissures can cause pain and bleeding, especially during bowel movements.

Fissures sometimes heal on their own. If they don’t, treatments include nitroglycerin cream, pain-relieving cream, and Botox injections to promote healing and ease discomfort. Surgery is an option for fissures that haven’t healed with other treatments.

The same breakouts that affect many teenagers can also be a problem in some people with Crohn’s disease. These skin eruptions aren’t from the disease itself, but from the steroids used to treat Crohn’s.

Steroids are usually prescribed only short-term to manage Crohn’s flares. Once you stop taking them, your skin should clear up.

Skin tags are flesh-colored growths that typically form in areas where skin rubs against skin, such as in the armpits or groin. In Crohn’s disease, they form around hemorrhoids or fissures in the anus where the skin is swollen.

Although skin tags are harmless, they may become irritated in the anal area when feces get stuck in them. Wiping well after each bowel movement and keeping the area clean can prevent irritation and pain.

Up to 50 percent of people with Crohn’s disease develop a fistula, which is a hollow connection between two parts of the body that shouldn’t be there. The fistula may connect the intestine to the skin of the buttocks or the vagina. A fistula can sometimes be a complication of surgery.

The fistula may look like a bump or boil and be very painful. Stool or fluid may drain from the opening.

Treatment for a fistula includes antibiotics or other medications. A severe fistula will need surgery to close up.

These painful sores form inside your mouth and cause pain when you eat or talk. Canker sores are the result of poor vitamin and mineral absorption in your GI tract from Crohn’s disease.

You may notice canker sores most when your disease is flaring. Managing your Crohn’s flares can help relieve them. An over-the-counter canker sore medication like Orajel will help to relieve the pain until they heal.

Small red and purple spots may be due to leukocytoclastic vasculitis, which is inflammation of the small blood vessels in the legs. This condition affects a small number of people with IBD and other autoimmune disorders.

The spots may be itchy or painful. They should heal within a few weeks. Doctors treat this condition with corticosteroids and drugs that suppress the immune system.

Epidermolysis bullosa acquisita is a disorder of the immune system that causes blisters to form on injured skin. The most common sites for these blisters are the hands, feet, knees, elbows, and ankles. When the blisters heal, they leave scars behind.

Doctors treat this condition with corticosteroids, drugs like dapsone that reduce inflammation, and medications that suppress the immune system. People who have these blisters need to be very careful and wear protective gear when they play sports or do other physical activities to avoid injury.

This skin disease causes red, flaky patches to appear on the skin. Like Crohn’s disease, psoriasis is an autoimmune condition. A problem with the immune system causes skin cells to multiply too quickly, and those excess cells build up on the skin.

People with Crohn’s disease are more likely to develop psoriasis. Two biologic drugs — infliximab (Remicade) and adalimumab (Humira) — treat both conditions.

Vitiligo causes patches of skin to lose their color. It happens when skin cells that produce the pigment melanin die or stop working.

Vitiligo is rare overall, but it’s more common in people with Crohn’s disease. Makeup can cover up the affected patches. Medications are also available to even out skin tone.

Small red and painful bumps on the arms, neck, head, or torso are a sign of Sweet’s syndrome. This skin condition is rare overall, but it can affect people with Crohn’s disease. Corticosteroid pills are the main treatment.

Report any new skin symptoms, from painful bumps to sores, to the doctor who treats your Crohn’s disease. Your doctor can either treat these issues directly or refer you to a dermatologist for treatment.