Picture of Alopecia Areata
A common hair loss condition, alopecia areata, usually starts as a single quarter-sized circle of perfectly smooth baldness. Alopecia patches often regrow in three to six months without treatment. Sometimes, hair regrows in white coloration. In another variant, alopecia areata can produce two or three bald patches. When these grow back, they may be replaced by others. The most extensive form of hair loss is called alopecia totalis, in which the entire scalp becomes bald. It's important to emphasize that patients who have localized hair loss generally don't lose hair throughout the scalp. Alopecia can affect hair on other parts of the body, too (for example, the beard).
Image Source: Images reprinted with permission from eMedicine.com, 2010.
Text: MedicineNet - Hair Loss in Men and Women