Hidradenitis suppurativa

Hidradenitis suppurativa (sometimes known as acne inversa) is a painful, long-term skin disease that causes abscesses and scarring on the skin – usually around the groin, buttocks, breasts and armpits.

It's not known exactly what causes hidradenitis suppurativa (HS), but the disease is linked to inflamed sweat glands and plugging of the hair follicles.

An estimated 1% of the population has HS – but this may be an underestimate, as some people might be too embarrassed to seek diagnosis and treatment.

What are the symptoms?

HS ranges from mild to severe.

It causes a mixture of red boil-like lumps, blackheads, cysts, scarring and channels in the skin that leak pus. These lumps and spots are found around the groin and armpits, and sometimes under the breasts and in other areas (see below). 

HS may sometimes be mistaken for acne, folliculitis (inflammation of the hair follicles) or a sexually transmitted infection (STI), such as herpes.

Some of the lumps may become infected with bacteria, causing a secondary infection that will require antibiotics to treat. HS is very painful.

The disease tends to start with a firm pea-sized lesion developing in one place. This either goes away on its own or ruptures after a few hours or days, to ooze pus.

Often, new lumps will soon appear in an area nearby. If these are not controlled with medication, larger lumps may form and spread. Narrow channels also form under the skin that break out on the surface and leak pus. These are called sinus tracts.

HS is a lifelong, recurring condition that requires constant management (see the Outlook section below).

Stages of the disease

Doctors classify the disease into three distinct stages:

• Stage 1 – single or a few isolated abscesses without scarring or sinus tracts.
• Stage 2 – recurrent abscesses in more than one area and the beginning of the formation of sinus tracts.
• Stage 3 – widespread abscesses with many interconnected sinus tracts under the skin. There may be severe scarring and continuous leaking.

Main affected areas

HS usually affects skin in the following areas:

• around the groin and genitals
• in the armpits
• around the bottom (anus)
• on the buttocks and inner thighs
• below the breasts

The abscesses may spread to the nape of the neck, waistband and inner thighs. Other isolated areas have been known, including the front or back of the legs, the sides, the back area and even the face.

Many people with HS develop a pilonidal sinus, which is a small hole or "tunnel" in the skin, usually at the top of the buttocks, where the buttocks separate. 

What are the causes?

The exact cause of HS is unclear, but the bumps and spots appear to be the result of blocked sweat glands and hair follicles.

However, the disease is not infectious and is not linked to poor hygiene.

It is thought that HS may be caused by a problem with the immune system. According to the British Association of Dermatologists, it may be linked to Crohn's disease. Many HS patients also suffer from another underlying autoimmune disorder (where the immune system attacks the body's own cells and tissues).

Who is affected?

HS usually starts around the age of puberty, but it can appear at any age.

It is less common for HS to occur before puberty or after the menopause, leading some experts to believe that the sex hormones have some sort of influence on the disease.

In around a third of cases, HS runs in families.

HS also affects more women than men, for reasons that are unclear.

Many people with HS:

• are smokers
• are overweight
• also have hirsutism (excessive hair growth) and/or acne, both of which are linked to levels of sex hormones 

Smoking and being obese are likely to make the condition worse.

How is it treated?

HS can be difficult to manage and there is no cure. The aim is to catch the disease in its early stages and prevent it getting worse. Therefore, an early diagnosis is important.

In the early stages, the disease may be controlled with medication. Persistent and severe cases may require surgery. These treatments are outlined below.

Antibiotics

If your lumps are particularly painful, red and oozing pus, your GP or specialist may prescribe a two-week course of antibiotic tablets, as there may be a secondary infection present.

If there is no suspected bacterial infection, antibiotics are used as suppressive treatment. This involves a course of antibiotics, usually lasting up to three months, with the aim of remission (a symptom-free period).

You may be prescribed a topical antibiotic cream, such as clindamycin 1%, to use twice daily. Oral antibiotics include erythromycin, tetracycline, lymecycline, doxycycline or clindamycin, alongside a number of other options.

Antiseptics

Antiseptic washes such as 4% chlorhexidine wash are frequently prescribed alongside other treatments.

Antiseptics are usually applied all over the body, except the head and neck, then washed off after a few minutes.

Retinoids

Retinoids are vitamin-A based drugs such as isotretinoin. They are not as effective for treating HS as they are for acne, but a course for 6 to 12 months may help to control some of the spots and lumps.

Isotretinoin should be used with caution, with the advice of a specialist. It cannot be taken during pregnancy, and possible side effects include dry lips, skin and eyes. 

Read more about the side effects of isotretinoin.

Contraceptive pill

Women whose HS flares up before their period may benefit from taking the contraceptive pill for 12 months or more.

The pill contains an artificial version of oestrogen, which should help reduce secretions from the sweat glands and control the lumps.

Immunosuppressive treatments

Severe cases of HS may require treatments that suppress the immune system, such as corticosteroids, ciclosporin and biological drugs.

Corticosteroids

You may be prescribed steroid medicine (corticosteroids) such as prednisolone to reduce severely inflamed skin. Corticosteroids can be taken as tablets, or you may have an injection of the drug directly into your affected skin.

Possible side effects of corticosteroids are fluid retention, weight gain, constipation and mood swings. 

Find out more about the side effects of corticosteroids.

Ciclosporin 

Ciclosporin is a powerful medication that suppresses the immune system. For some patients with HS, it can relieve symptoms for a few months.

However, this medicine can cause vomiting, diarrhoea, high blood pressure, numbness, and kidney and liver problems. 

Learn more about the side effects of ciclosporin.

Infliximab and adalimumab

Biological drugs like infliximab or adalimumab, which also suppress the immune system, may be prescribed for severe cases of HS. Your dermatologist will usually only prescribe them if other treatments don't work.

Infliximab and adalimumab are given by injection at a hospital or clinic. You may need to have the injections at regular intervals.

Possible side effects include blood disorders, infection and cancer of an organ. Speak to your doctor about these side effects if you are considering taking this medication.

Surgery

A surgical procedure may be considered if your HS is not controlled with medication, or suddenly becomes worse.

If you have some very large lumps that will not clear with antibiotics, you may be offered one of the following treatments:

• incision and drainage or removal – cutting off the lids of the lumps, and draining or scraping out the contents inside, or removing the lumps altogether
• laser ablation – using a laser to remove the lumps (this has no proven benefit and is an experimental treatment)
• cryotherapy – freezing off the lumps with liquid nitrogen

Outlook

HS persists for many years and there is no cure, but symptoms may be improved with treatment if it is diagnosed early.

Not all people with HS progress to stage 3 – the disease can be controlled so it doesn't progress beyond stage 1.

However, HS can affect your life in many ways. Routinely changing dressings and living with the pain, discomfort and embarrassment of the symptoms can affect quality of life and lead to stress, anxiety and depression.

If you are having problems coping, speak to your health professional or a charity to see what support is available. 

Read about how to find mental health support.