Studi e statistiche parlano di circa 2-4 milioni di persone in tutto il mondo che nell’arco della propria vita possono andare incontro a questa forma di alopecia (tra lo 0,05% e lo 0,1% della popolazione).
Of course, these figures are only estimates based on regional studies, and cover all forms of AA from small patches of hair loss through to alopecia universalis. The actual expression of AA in a population probably varies from region to region. Information on how AA affects different groups of people is lacking but, as an example, it is believed that AA is slightly more common in Japanese people – particularly people of Japanese decent living in Hawaii (Arnold 1952). A recent study has put the average lifetime risk of experiencing AA at 1.7%, considerably higher than most previous estimates at around 1% (Safavi 1995).
There are two schools of thought as to what extent AA affects males and females. Either AA affects males and females in equal numbers or it affects a greater number of women. There have been claims that the female to male ratio is between 1:1 (Muller 1963, Safavi 1995) and 2:1 (Friedman 1985). In most other autoimmune diseases, a greater number of women are affected with ratios of up to 10:1 for Systemic Lupus Erythematosus (SLE) (Ollier 1989). This is believed to be due in part to differences in hormone levels between the two sexes.
The first expression of AA is most likely to occur in people in their teenage years or early twenties (Gollinck 1990), but individual cases have been reported in children younger than two years of age or older than 70 years (Muller 1963). Between approximately 10% and 25% of patients show a family history of AA. With 10% quoted by Muller (1963), 11% by De Weert (1984), 18% by De Waard-van der Spek (1989) and 24% by Friedman (1981) – among others.
The vast majority of patients with AA are in excellent health and have no associated clinical conditions but a number of diseases have been reported showing increased prevalence in conjunction with AA for a minority of people. These include Down’s syndrome (Du Vivier 1975), Addison’s disease (Kern 1974, Zauli 1975), thyroid disorders (Muller 1963, Cunliffe 1969) and vitiligo (Muller 1963, Cunliffe 1969, Main 1975) among other conditions.