It can be easy to confuse hidradenitis suppurativa (HS) with pilonidal cysts, or pockets in the skin that usually contain hair and skin cells and develop near the tailbone. However, they’re different skin conditions that may require different treatments.

Knowing how the two conditions differ, including their symptoms, can help you know when to see your dermatologist. Here are some key differences that can help make sure both conditions are recognized and treated.

Also known as acne inversa, HS usually occurs in areas where skin rubs together, such as the groin and armpits. These areas can also contain many sweat glands. HS can also develop in areas with thick, coarse hair.

HS can also appear under the breasts, on the inner thighs, and on the buttocks. Less commonly, HS may develop near the ears or around the belly button as well as on the face, back, and neck.

Pilonidal cysts, on the other hand, develop almost exclusively near the tailbone, at the top of the cleft between the buttocks. Unlike HS, pilonidal cysts don’t typically form elsewhere on the body.

What Does a Pilonidal Cyst Look Like Compared With HS?

HS may first appear as pairs of blackheads (bumps with dark centers) or as pea-sized lumps under the skin. These bumps may last for days to months and can be painful or itchy. Over time, some lumps may get bigger, break open, and drain blood and pus.

Pilonidal cysts can cause lumps under the skin, but you may not notice them at first. The cysts usually develop when hair punctures the skin and becomes embedded, creating a pocket that can fill with hair and dead skin cells.

If this pocket in the skin becomes infected, a pilonidal abscess may form. Symptoms can include swelling, pain, discolored skin, and drainage.

HS bumps can form tunnels under the skin called sinus tracts, which may drain. Pilonidal disease can also form sinus tracts under the skin.

The exact cause of HS isn’t fully understood, but an overactive immune system plays a role in the inflammation linked to the condition. This inflammation can cause a mix of sores, changes in skin color, swelling, itching, pain, and drainage.

Researchers aren’t sure exactly what triggers HS, but there may be a genetic link. An estimated 1 in 3 people with HS have a family member with the condition.

Regardless of the cause, it’s important to know that HS isn’t caused by poor hygiene or sexually transmitted infections. It’s not contagious, nor is it an infection, even if bacteria are found in the area.

It’s not known just what triggers pilonidal cysts to form, either. Hair that gets stuck under the skin or becomes ingrown may play a role. Friction and pressure from tight clothing or sitting for long periods may also contribute.

HS and pilonidal cysts are considered separate conditions, but they can occur together. Pilonidal disease frequently happens alongside HS, and both are part of a group of related conditions called the follicular occlusion tetrad. Researchers are continuing to study their connection.

It’s possible to have both HS and pilonidal cysts. The conditions share some risk factors but also have some different ones. Here’s how they compare, according to Mayo Clinic and DermNet:

Both HS and pilonidal cysts can involve lumps under your skin that can become painful, but they tend to look different and occur in different locations. Your dermatologist will look for these differences to help make a diagnosis.

They’ll begin by asking about your medical history, focusing on your family history and other skin conditions. They’ll also perform a thorough examination of the affected skin, noting where the lesions are and what they look like.

Your healthcare provider may also ask when your symptoms first appeared, how long they last, and whether they go away and come back. Keep in mind that no lab tests are designed to diagnose HS or pilonidal cysts.

If your lesions are draining, your doctor may take a sample to check for bacteria. For pilonidal cysts, your doctor may also order a CT scan or MRI to look for sinus tracts, especially if surgery is being considered.

HS and pilonidal cysts have different treatment plans. For instance, HS may be treated with biologics, which target parts of the immune system to reduce inflammation.

Pilonidal cysts aren’t typically treated with biologics. Pilonidal disease is thought to develop when hair becomes embedded in the skin, causing inflammation.

Sometimes, an infected pilonidal cyst needs to be drained, which can often be done in a healthcare provider’s office. If pilonidal disease keeps coming back or is severe, surgery may be needed.

Other treatments, such as phenol injections, may help reduce the incidence of cysts and abscesses. Hair removal may also be recommended to help reduce the risk of pilonidal disease coming back.

Whether you’re treating HS or pilonidal cysts, your healthcare provider can recommend a treatment plan based on your condition and its stage. Together, you can come up with a plan that helps ease your discomfort and addresses your main concerns.