Common causes of patchy hair loss are: alopecia areata (patches of baldness that usually grow back) traction alopecia (thinning from tight braids or ponytails) trichotillomania (the habit of twisting or pulling hair out) tinea capitis (fungal infection). The amount and patterns of baldness can vary greatly; it ranges from male and female pattern alopecia (androgenic alopecia, also called androgenetic alopecia or alopecia androgenetica), alopecia areata, which involves the loss of some of the hair from the head, and alopecia totalis, which involves the loss of all head hair, to the most extreme form, alopecia universalis, which involves the loss of all hair from the head and the body.

The problem of hair loss has resulted in many other myths and misconceptions. For instance, wearing hats does not "choke off" hair roots and promote baldness. Likewise, longer hair does not put a strain on roots. Most hair loss is not associated with systemic or internal disease, nor is poor diet a frequent factor. Thyroid disease can cause hair loss, but thyroid tests on people who have ordinary hair loss are usually normal. Although many medications list "hair loss" among their potential side effects, drugs are also not overall common causes of thinning or lost hair. On the other hand, with cancer treatments and immune suppression medications, hair loss is not uncommon.

Male hair loss is genetically determined (passed on from parents). Although a doctor can offer medical treatment to improve the condition, this may have side effects. Hair loss is not a disease but a very general problem wherein a poor diet is a frequent factor. Thyroid disease can cause hair loss, but thyroid tests on people who have ordinary hair loss are usually normal. Although many medications list "hair loss" among their potential side effects, drugs are also not overall common causes of thinning or lost hair. On the other hand, with cancer treatments and immune suppression medications, hair loss is not uncommon.

There are many causes of scalp hair loss. This article will cover the common ones. Baldness involves the state of lacking hair where it often grows, especially on the head. The most common form of baldness is a progressive hair thinning condition called androgenic alopecia or "male pattern baldness" that occurs in adult male humans and other species. The amount and patterns of baldness can vary greatly; it ranges from male and female pattern alopecia (androgenic alopecia, also called androgenetic alopecia or alopecia androgenetica), alopecia areata, which involves the loss of some of the hair from the head, and alopecia totalis, which involves the loss of all head hair, to the most extreme form, alopecia universalis, which involves the loss of all hair from the head and the body.

Some hair loss sufferers make use of clinically proven treatments such as finasteride and topically applied minoxidil (in solution) in an attempt to prevent further loss and regrow hair. As a general rule, it is easier to maintain remaining hair than it is to regrow; however, the treatments mentioned may prevent hair loss from Androgenetic alopecia, and there are new technologies in cosmetic transplant surgery and hair replacement systems that can be completely undetectable. In the USA, there are only two drug-based treatments that have been approved by the U.S. Food and Drug Administration (FDA)

There is one useful way to classify hair loss is by whether the loss is localized and patchy, or whether it affects large areas or the whole scalp.