I. Introduction

Hidradenitis suppurativa (HS) is a chronic skin disease that causes recurrent painful boils. HS was originally considered a very rare disease, but over the past decade, research on HS has dramatically increased and we now know that HS is not rare. In this chapter, we will discuss how common HS is, who is more likely to get it, risk factors, and current challenges in the world of HS.

II. Epidemiology

Epidemiology is the study of the distribution (how common is a disease, where in the world is it the most common) and determinants (causes and risk factors) of diseases in different populations. Below we will discuss the epidemiology of HS.

Prevalence and Incidence

Prevalence is the percentage of people who have a disease. Research on large populations have shown that, overall, about 0.1% to 4% of people have HS worldwide. These studies were done in different populations of the world, accounting for a wide range of percentages. The true prevalence is likely higher than the reported percentages, because of common instances of HS underdiagnosis or misdiagnosis.

The incidence of a disease is a percentage that tells us how many people are newly diagnosed with a disease every year. Recent studies have shown that HS has an incidence of 0.01%- 0.03%. The incidence of HS may rise as awareness of HS increases and more people are properly diagnosed.

Demographics

Gender. Research done in several countries has generally shown that in Western nations, twice as many women have HS compared to men. Interestingly, researchers in Asia (Korea and Japan) found the opposite was true, with almost twice as many men having HS. Overall, more women have been found to have HS, but this may vary depending on where you live in the world.

Race. HS affects people of all races. However, African Americans are disproportionately affected by HS. A study done in the United States found that African American patients were three times more likely to have HS compared to White patients. African Americans were also more likely to consult healthcare providers at a more advanced stage of HS. There has been less HS research done in Africa, Asia, and South America. More studies are needed to determine how common HS is in different races.

Age. HS is most common in people in their 20s and 30s. Women tend to develop HS earlier than men, possibly due to their earlier onset of puberty. Some studies have shown that a certain subset of people develop HS before the age of 18, which is considered “early onset.” People may also develop the disease later in their life, after the age of 40, which is considered “late onset.”

Risk Factors

Risk factor is a term used to describe something that may increase your risk of developing a disease. There are risk factors that are non-modifiable, which means they are inherent traits you cannot change. There are also risk factors that are modifiable, which means they can be changed with lifestyle choices. Non-modifiable risk factors for HS include family history and genetics. Modifiable risk factors include smoking, obesity, skin friction, and diet. In Chapter 14, we will discuss why these risk factors increase HS disease, and how to improve your HS symptoms by making lifestyle changes to decrease your modifiable risk factors.

III. Clinical Presentation and Diagnostic Challenges

The diagnosis of HS is based on how it presents clinically, meaning that a healthcare provider can diagnose you with HS by asking about your symptoms and examining your skin with a physical exam. There are three main things they consider:

1. How the lesions look.
2. Where the lesions are located (usually located in the skin fold areas, although it can be present in non-skin fold areas as well).
3. How often the lesions occur (at least two flares in a six month period).

Further information on clues that you might have HS can be found in Chapter 2.

IV. Causes of HS

Although the exact of cause HS is not yet known, we know that HS is caused by a combination of several factors. These are discussed in detail in Chapters 3 and 4.

V. HS Burden, Comorbidities, Disease Complications

HS can put a huge physical and mental burden on people, affecting their overall quality of life. The impact of HS on mental health, daily activities, and sexual health is discussed in Chapter 5.

HS comorbidities, or diseases that are associated with HS, can range from being very common to rare. Some of the common comorbidities include metabolic conditions such as obesity, high cholesterol, high blood pressure, diabetes, and polycystic ovarian syndrome (PCOS). Chapter 6 discusses both common and uncommon diseases associated with HS.

Over time, HS may cause medical complications that occur on the skin and also throughout the body. Common medical complications of HS are discussed in Chapter 7.

VI. Special Populations

Women, especially of childbearing age, are disproportionately affected by HS. Because of this, women face unique challenges in dealing with and treating HS because of factors such as menses, pregnancy, breastfeeding, and menopause. Specific considerations for women living with HS are discussed in Chapter 8.

Children, even those who have not yet reached puberty, can also develop HS. Often, children who develop the condition have a family member with HS, suggesting a genetic component. Treating children can be challenging because most of the current available medications were studied in adult populations. HS in children is further discussed in Chapter 9.

VII. HS Management

While there is currently no cure for HS, there are ways to control your disease.

The goal of HS treatment is to treat ongoing flares and pain, and to reduce the number of future flares through preventative treatment.

It is important to communicate with your healthcare provider when you feel something is working (or not working) for you. Chapter 11, 12, and 26 discuss how to make the most of your HS visits (including how to track your HS journey) and how to set your treatment goals. The same treatment might not work for everyone therefore, it is important to create an individualized plan. Chapter 25 discusses how to create an effective treatment plan with your healthcare provider.

Types of treatment options available to treat HS include:

Topical medications: medications and washes applied onto the skin. Chapter 15 discusses skin and wound care and Chapter 16 discusses topical medications and washes.

Systemic medications: medications taken by mouth or injected through the skin. Chapter 17 discusses oral antibiotics, Chapter 18 discusses other oral medications that are not antibiotics, and Chapter 19 discusses systemic medications called biologics.

Procedural treatments: Chapter 21 discusses how to know when surgery for HS is right for you. Chapter 22 discusses surgical excisions done in the operating room while Chapter 23 discusses procedures for HS that can be done in the office. Chapter 24 discusses laser treatments for HS.

HS often requires a team of healthcare providers that specialize in different areas of medicine. Specialists commonly involved in the care of people living with HS include dermatologists, wound care specialists, pain management physicians, mental health professionals, surgeons, and nutritionists. Chapter 13 goes into detail on specialists who may be on your care team and their roles. Chapter 20 discusses pain control for HS.

Managing the different aspects of HS care can become expensive Chapter 10 has tips on how to manage HS on a budget.

VIII. Experiences from People Living with HS and also HS Caregivers

Connecting with others who have HS can be very helpful for people with HS. Chapters 27 and 28 are dedicated to describing the experiences from people with HS, who themselves are leaders in HS advocacy.

IX. Looking to the Future

Research on HS has grown rapidly in the past decade. However, there are still many challenges to overcome. Some of these challenges include not understanding the exact cause of HS, lack of awareness among the general public and medical community, missed and delayed diagnoses, and limited treatment options. As our understanding of causes of HS improves, it will help us develop new treatments to target those causes. We are hopeful that more effective treatments will become available in the upcoming years. Chapter 29 discusses new medications for HS that are in development and being studied in clinical trials (also known as medications in the “pipeline”). Chapter 30 discusses what the future of HS will look like.