Alopecia Areata is an extremely common condition and will affect 1% to 2% of the population at some point in their lives. Most sufferers are children and young adults (below 40 years old), though it can affect people of all ages. The hair loss is sudden and manifests itself in small, smooth-skinned patches that are likely to gradually widen with time. It can also affect the sufferer's nails, giving them a pitted, ridged or brittle appearance. The exact cause is still unknown, although current theories include an auto-immune disease, stress or suggest a genetic basis.