It is important to define hair. Hair is actually a part of our body, which is scientifically dead after it grows out of the hair bearing skin/scalp. Because the hair grows inside a skin, we can see the hair as a whole.
In hair diseases the structure of the hair and the hair follicle are damaged. The diseases that damage the hair follicle can mainly be scalp diseases or hair loss conditions.
There are many reasons for hair loss. The male pattern hair loss is seen in both men and women. In women, in some cases the hair is lost with the hair follicles. Women also experience hair loss after giving birth. Nowadays there are very strict and intense weight loss programs. After losing weight rapidly, about 3 months later, one might experience hair loss. There are also diseases of the hair shaft itself. Hair shaft is the part of hair that sticks out of the skin.
The hair shaft might split and cause some hair loss. Even the graying of the hair can be considered a type of hair disease. The hair having gone through several chemical procedures can cause diseases too. Other than these, there are also genetic hair diseases.
For instance, the hair might be matted, and it might not be regularly straight. When you observe them under a microscope, you can see some tiny bumps. These are caused by genetic disorders. The hair and the teeth often develop at the same time in the womb. Often times, when a person has some genetic hair disorders, they will have tooth disorders too.