How many types of baldness are there according to the study?

Some people are troubled by the absence of hair on their heads. People who study this phenomenon divide baldness into five main types. A general thinning of the hair is called partial baldness and an absence of hair in area usually covered by hair is labeled area baldness. A thinning of the hair which occurs in persons after about fifty years of age is called old age baldness. Young people may experience what is called premature baldness. And when certain areas of the head become bald while hair over the rest of the head continues to grow at a normal rate, the condition is called pattern baldness.
    Despite all the research that has been done on the subject, the specific causes of baldness are still unknown. Experts believe that heredity, aging, hormone imbalance and infection have an effect on the loss of hair. The most widespread cause of baldness is heredity, but it affects female members of a family less than males. The women of a bald family are more apt to retain their hair than the men. The females, however, pass on an inherited tendency toward baldness to their male off-spring.
    Besides the possible causes mentioned above, baldness may result from some infections and diseases. However, this type of baldness is usually not permanent. Proper cleaning has been found to be an important factor in baldness. An improper cleaning of the head may accelerate baldness, while the stimulation from cleaning and brushing helps to delay it.