Erin Markel, age 10, of Orlando, Fla., for her question:

WHY IS MY DAD BALD?

Baldness is the absence of hair on the head. The exact causes of baldness are not known. Scientists, however, think that infection, hormone imbalance, aging and heredity can affect baldness.

Inheritance is the most common cause of baldness, and it affects males more than females. So your dad is probably bald because his dad and grandfather were also bald.

While women of a bald family are somewhat liable to baldness, they are more likely to retain their hair than are the men. But they pass on to their sons the inherited tendency toward baldness. So perhaps your grandmother passed on the tendency to your dad.

One striking form is premature baldness that develops in young people. It proceeds unevenly. Certain areas become nearly bald. But the hair continues to grow at a normal rate over the rest of the scalp. This kind of hair loss is often called pattern baldness.

Partial baldness is a thinning of the hair. Area baldness is the absence of hair from areas that are normally covered by hair, such as the forehead and top of the head. Senile baldness is the thinning of hair which occurs in older years.

Also part of baldness is the tendency with age of the hairline to recede.