Severe illnesses (usually with high fever) and medications can both cause temporary loss of hair, known as telogen effluvium. In some cases the loss can be delayed, so before panicking, thoroughly re-evaluate your recent history and discuss possibilities with your doctor. The drugs that may promote this temporary hair loss include birth control pills, other hormones, anticoagulants, allopurinol, some anti-inflammatory drugs and some blood pressure medications, plus, of course, cancer-therapy drugs. Vitamin A is sometimes mentioned as causing hair loss, but that requires far higher doses than most people would normally take. (Incidentally, vitamin A is actually necessary for proper skin and hair formation.)

A striking, and not uncommon, loss of hair comes in the form of alopecia areata: the rapid loss of patches of hair, usually coin-sized, while surrounding areas of hair appear normal. The cause is still basically unknown, though the prevailing theory implicates an immune-system problem. The hair tends to return at intervals, but recurrences are common. The worst case is total loss (areata totalis), which can even include eye and body hair.

If scaling is present, though, it is possible that ringworm is causing the patchy hair loss, masquerading as alopecia areata. Here again, careful analysis is needed. Ringworm is readily treatable with antifungal agents.

Other reversible causes of hair loss include traction alopecia, which is the loss of hair due to its continually being pulled by certain hairstyles, such as tight braiding or ponytails, or by the unconscious habit of twisting the hair. Take care in your choice of fashion and in how hard your hair is pulled.