Pseudofolliculitis Barbae

A number sign (#) is used with this entry because pseudofolliculitis barbae (PFB) is associated with a polymorphism in the KRT75 gene (609025).

Clinical Features

Pseudofolliculitis barbae, also termed pili incarnati, 'ingrown hairs,' or 'razor bumps,' is a common human hair disorder that can occur in anyone who has curly hair and shaves. It most commonly occurs in the facial beard area, but can also occur on the scalp, neck, and groin. Regular shaving, in particular against the grain, is usually the precipitating factor in this disease. The razor produces short, sharp, and pointed hairs that penetrate the skin either in an extra- or transfollicular manner. These ingrowing hairs initiate a foreign body reaction producing erythematous papules and pustules that may heal with or without scarring and may produce keloid formation. Compared to Caucasian males, African American males are more susceptible to developing PFB due to their genetic predisposition for strongly curved hairs (Crutchfield, 1998; Winter et al., 2004).

Ross et al. (1993) reported a 24-year-old Caucasian male with pseudofolliculitis barbae confined to the right inframandibular region. The rash promptly subsided after 3 to 4 days without shaving but his employer's regulations required him to be clean-shaven. Physical examination of his right mandible showed that the lesions were confined to an area where the hairs grew downward as part of a 'beard whorl.' The individual hairs were not curved or coarse. The patient admitted to shaving against the grain but in this area it would be impossible to be clean-shaven due to the whorl. Ross et al. (1993) noted that the presence of the whorl in this patient contributed to the disorder, and emphasized the importance of identifying symptomatic beard whorls in men with PFB.

Molecular Genetics

In 2 affected members of a Caucasian family with pseudofolliculitis barbae, Winter et al. (2004) identified a heterozygous SNP in the KRT75 gene (A12T; 609025.0001). In a larger group of 200 individuals, Winter et al. (2004) found that the A12T SNP was present in 9% of individuals without the disorder and 35% with the disorder, which was a significant association (p less than 6 x 10(-6)). The incidence of the A12T substitution in the investigated population was approximately 3 times higher in African Americans compared to Caucasians (36.7% vs 10.9%). Subsequent regression analysis showed that the presence of curved hair follicles and the A12T substitution represented independent risk factors for the condition, with the A12T SNP yielding an odds ratio of 6.12. However, there was a more than 50 times higher risk of developing PFB in the presence of curly hair.

Population Genetics

Among 110 Caucasians and 90 African Americans, Winter et al. (2004) found a much higher incidence of PFB in the black population (82%) compared to the white population (18%). A minority of PFB-affected individuals were black (7%) and white women (3%), who noted PFB symptoms after shaving in the groin and/or the axilla.