First of all, blame your parents. Scientists say genetics probably plays a role in the graying process. This could explain why some people encounter their first silver strand in their 20s and 30s while others are lucky enough to avoid it until their 70s or 80s.

Family predisposition, however, doesn't explain all cases. A person's diet may have something to do with it. You are what you eat, If you're not going to feed your body well on the inside, what's coming out is not going to be high quality."

The type of foods people eat can affect the shine and texture of their hair, but the exact part nutrients play in hair graying. B vitamins can help keep hair follicles healthy, she explains, but there is no evidence such vitamins have an effect on pigmentation.

Poor nutrition could explain hair pigmentation loss in some populations. A condition called Kwashiorkor, for example, results from severe protein deficiency. This illness, which includes the discoloration or loss of hair, is commonly seen in countries that are underdeveloped, or stricken with war or famine. It is also not unusual to see this ailment in people with eating disorders such as anorexia.

Other medical conditions that could cause tresses to gray reportedly include congenital and premature aging syndromes. Progeria, for instance, is a disease that makes people age a lot faster than normal. In one such case at dermatologist Bruce Katz's office, a patient had hair that turned gray in her teens.

Normally hair grows in three different phases: the growing, transitional and resting stages. Colored hair takes about 1-3 years to grow, he says, and then goes into the transitional phase. At the resting phase, the hairs fall because the new strands push them out as they surface. When no more melanin is produced in the hair follicle, the new hairs come out gray.

Besides dyeing hair a different color, there are no treatments at this time for graying manes. But hair transplants are possible for people who still have their natural-colored hair elsewhere on their scalp. This treatment has been used to help people get rid of baldness, but has not been implemented to grow new hair with natural pigmentation.

For a select group of people, silver hair may be a temporary state, a few drugs may temporarily affect hair coloration. Anti-malaria medications that some traveling people take, have been known to discolor hair.

Anyone who may suspect that their hair quality or color may be affected by the medicines they use is urged to talk to their doctor.

All reasons for graying, however, may pale compared to the popular perception that stress is the culprit. Stress is known to deteriorate the body's immune system and to weaken its ability to fight bacteria or viruses.