Other than digestion, Crohn’s disease most commonly affects the skin. The reasons it can cause a rash are still poorly understood, but it may be due to the direct effects of the disease, immune factors, or a reaction to a medication.

Crohn’s disease is a type of inflammatory bowel disease (IBD). People with Crohn’s disease experience inflammation in their digestive tract, which can lead to symptoms like:

It’s estimated that up to 40 percent of people with Crohn’s disease experience symptoms that don’t involve the digestive tract.

The most common area where symptoms occur outside of the digestive tract is the skin.

Keep reading to learn more about Crohn’s disease and the skin.

People with Crohn’s disease can develop a variety of different skin lesions. Let’s explore some of them in more detail below.

Perianal lesions

Perianal lesions are located around the anus. They can be:

  • red
  • swollen
  • painful sometimes

Perianal lesions can take on a variety of appearances, including:

Oral lesions

Lesions may also occur in the mouth. When oral lesions appear, you may notice painful ulcers in the inside of your mouth, particularly on the inside of the cheeks or lips.

Sometimes other symptoms may be present, including:

  • a split lip
  • red or cracked patches at the corners of the mouth, which is called angular cheilitis
  • swollen lips or gums

Metastatic Crohn’s disease

Metastatic Crohn’s disease is rare.

The most common sites affected are the:

  • face
  • genitals
  • extremities

It may also be found in areas where two patches of skin rub together.

These lesions are typically plaque-like in appearance, although in some cases they may look more like ulcers. They’re reddish or purplish in color. Metastatic lesions may appear by themselves or in groups.

Erythema nodosum

Erythema nodosum is characterized by tender red bumps or nodules that occur just under the skin.

They’re often found on your lower extremities, particularly on the front of your shin. Fever, chills, aches, and pains may also occur.

Erythema nodosum is the most common skin manifestation of Crohn’s disease. It also often, but not always, coincides with a flare-up.

Pyoderma gangrenosum

This condition starts with a bump on the skin that eventually develops into a sore or ulcer with a yellowish base. You can have a single pyoderma gangrenosum lesion or many lesions. The most common location is the legs.

Like erythema nodosum, pyoderma gangrenosum can often happen during a flare-up. When the lesions do heal, there can be significant scarring. About 35 percent of people can experience a relapse.

Sweet’s syndrome

Sweet’s syndrome involves tender red papules that typically cover your head, torso, and arms. They can occur separately or grow together to form a plaque.

Other symptoms of sweet’s syndrome include:

Some other conditions are associated with Crohn’s disease and may also cause skin symptoms. Some examples include:

Reactions to drugs

In some cases, skin lesions are found in people taking a type of biologic medication called an anti-TNF drug. These lesions look like eczema or psoriasis.

Vitamin deficiencies

Crohn’s disease can lead to malnutrition, including vitamin deficiencies. A variety of these can cause skin symptoms. Examples include:

  • Zinc deficiency. Zinc deficiency causes red patches or plaques that may also have pustules.
  • Iron deficiency. Iron deficiency causes red, cracked patches at the corners of the mouth.
  • Vitamin C deficiency. Vitamin C deficiency causes bleeding under the skin, which causes bruise-like spots to appear.

The skin symptoms associated with Crohn’s disease can appear very diverse, depending on their type and location.

Scroll through the following pictures for some examples.

It’s not well understood how exactly Crohn’s disease causes skin symptoms. Researchers continue to investigate this question.

This is what we do know:

  • Some lesions, such as perianal and metastatic lesions, seem to be caused directly by Crohn’s disease. When biopsied and examined with a microscope, the lesions have similar features to the underlying digestive disease.
  • Other lesions, such as erythema nodosum and pyoderma gangrenosum, are believed to share disease mechanisms with Crohn’s disease.
  • Some autoimmune conditions that cause skin symptoms, like psoriasis and SLE, are associated with Crohn’s disease.
  • Secondary factors related to Crohn’s disease, such as malnutrition and medications used in treatment, can also cause skin symptoms.

So how could this all fit together? Like other autoimmune conditions, Crohn’s disease involves the body’s immune system attacking healthy cells. This is what leads to the inflammation associated with the condition.

Animal studies have shown that an immune cell called a Th17 cell is important in Crohn’s disease. Th17 cells are also associated with other autoimmune conditions, including those that can affect the skin.

As such, these cells could possibly be a link between Crohn’s disease and many of its associated skin symptoms.

Other studies suggest there are more immune factors associated with the disease.

However, additional research is needed to address the link between Crohn’s disease and the skin.

There are a variety of potential treatments for skin lesions that are related to Crohn’s disease. The specific treatment that you receive will depend on the type of skin lesions that you have.

Sometimes medications can help to ease skin symptoms. Some examples of medications that your healthcare provider may prescribe include:

Other potential treatments include:

  • discontinuing an anti-TNF biologic if it’s causing skin symptoms
  • suggesting vitamin supplements when malnutrition has caused a vitamin deficiency
  • performing surgery to remove a severe fistula, or fistulotomy

In some cases, skin symptoms may occur as a part of a Crohn’s disease flare-up. When this happens, managing the flare-up can also help to ease skin symptoms.

If you have Crohn’s disease and develop skin symptoms that you believe are related to your condition, make an appointment with your healthcare provider.

They may need to take a biopsy to determine what’s causing your symptoms.

Generally speaking, it’s always a good rule of thumb to see your healthcare provider if you notice skin symptoms that:

  • cover a large area
  • spread quickly
  • are painful
  • have blisters or fluid drainage
  • occur with a fever

Many people with Crohn’s disease will experience symptoms that affect areas other than the digestive tract.

One of these areas is the skin.

There are many different types of skin lesions associated with Crohn’s disease. These can occur because of:

  • direct effects of the disease
  • certain immune factors associated with the disease
  • complications associated with the disease, such as malnutrition

Treatment can depend on the type of lesion. It may often involve taking a medication to help relieve your symptoms.

If you have Crohn’s disease and notice skin symptoms that you think may be related, see your healthcare provider.

Read this article in Spanish.