How Common Is Folliculitis Decalvans and Who Gets It?

Quinquaud folliculitis decalvans (FD) is a rare, chronic inflammatory condition that causes painful pustules and can permanently damage hair follicles, leading to scarring hair loss. Because it is so rare, there is no exact figure for how many people in the general population have it ^[1]. Based on data from specialist referral clinics, FD accounts for a very small percentage of all hair loss cases ^[2]. While anyone can develop FD, larger studies suggest it is more common in men than in women, and patients are typically in their 30s or 40s when evaluated by a specialist ^[3][4]. However, these demographic patterns are general trends rather than strict rules for diagnosis.

How Common Is FD?

Because FD is uncommon, national health registries often lack a specific coding category for it. Instead, they usually group it together with other forms of primary cicatricial alopecia (scarring hair loss) ^[1]. As a result, the exact population-wide prevalence (the total number of existing cases in the general public) and incidence (the number of newly diagnosed cases each year) are unknown ^[1].

Instead, researchers estimate its frequency based on the types of patients who visit specialized referral clinics. These clinic-based percentages should not be interpreted as the lifetime risk for a person in the general population, nor do they represent an individual’s probability of being diagnosed with FD. The percentages vary widely depending on the clinic’s location, the types of patients they see, and the specific group being studied:

• Among general hair loss (alopecia) diagnoses: In a multinational study of over 2,800 patients at specialist hair clinics, FD accounted for just 2.8% of all hair loss diagnoses ^[2]. A regional clinic in Mexico found it made up 3.39% of their nearly 1,900 acquired hair loss cases ^[5].
• Among scalp disorders: Clinics in Benin and Israel reported that FD made up between 3.3% and 6.6% of patients seen specifically for various scalp or hair disorders ^[6][7].
• Among scarring hair loss: If a patient is already diagnosed with a scarring form of hair loss, FD makes up a larger share of those specific cases. Studies of these patients show that FD accounted for roughly 8% to 12% of scarring alopecia diagnoses in particular clinic series ^[8][9].

Who Typically Gets It?

While anyone can develop FD, researchers have observed a few demographic trends among those who seek treatment at specialty centers.

Sex

In larger, FD-specific studies, the condition shows a male predominance. In two multicenter studies, men made up approximately 60% to 63% of the patients ^[3][4]. However, women certainly do develop FD, and some smaller clinic studies have reported roughly equal numbers of men and women ^[10].

Age

Patients in clinical studies are typically in mid-adulthood. The average or median age of patients at the time of their clinic visit ranges between 35 and 40 years old ^[3][4][10]. It is important to note that this reflects the age at which patients are assessed by specialists, not necessarily the age when their symptoms first began ^[3]. While symptom onset in childhood or early youth is possible and has been reported, the exact frequency of early onset remains unclear because it is not consistently recorded ^[11].

Geography and Ethnicity

Available studies have not established a strong ethnic or geographic pattern for FD ^[8]. It has been reported in diverse populations worldwide, including in patient cohorts from Jamaica, Morocco, Taiwan, and Mexico ^{[12][10][13][5]}. Because most information comes from specialized referral centers, comparisons between different ethnicities or regions can be distorted by differences in clinic access, referral patterns, and underrepresentation of certain groups ^[2].

Understanding the Limitations

When reading about who gets FD, it is crucial to remember the limits of current medical research. Because FD is rare, most studies rely on small groups of patients (often fewer than 100 people) ^[4][14][10].

These demographic statistics are useful for understanding the disease generally, but they cannot diagnose or exclude FD for an individual. Your age, sex, ethnicity, and country cannot confirm or rule out the condition. If you are female, very young, or belong to a demographic not often featured in studies, you can still develop FD. A diagnosis depends primarily on the physical pattern on the scalp, your symptoms, and specialized examinations rather than your demographic profile.