Hair loss, or alopecia, has many different causes. Figuring out what is causing your hair loss involves a careful medical history, a review of your hair care practices, an examination of the hair and scalp, blood tests, and sometimes a scalp biopsy.
Everyone is born with a set number of hair follicles, and no new ones are created after birth. Each scalp hair follicle produces an individual hair, called a hair shaft. Hair follicles produce hair shafts in a repeated cycle, each of which lasts several years. After every cycle the hair shaft falls out as the hair follicle produces a new one. Thus, it is normal to lose approximately 100 hairs a day.
Sometimes this random cycle becomes synchronized resulting in a temporary hair loss, called a telogen effluvium (see photo below). This has a sudden onset, occurs three months following a stressful medical or emotional condition, and involves the entire scalp in an even fashion, causing shedding of hair and sometimes thinning all over. Examples of things that can cause a telogen effluvium are childbirth, after rapid weight loss, following surgery, or experiencing death of a family member. Certain diseases such as thyroid conditions and medications can also cause hair loss due to abnormal cycling. This type of hair loss tends to resolve spontaneously after several months, but can sometimes persist.
A common cause of hair shedding is genetic, known as androgenetic alopecia or male or female pattern hair loss (see photos). While well recognized in men as balding, women are often not aware that they can also be affected. This condition is inherited from either side of the family, and in women presents with hair loss on the top of the head and/or the temples. This condition can be treated with minoxidil and low level laser light.
Damage to the hair shaft itself can cause breakage of the hair (see photo). Short pieces of hair may fall out in the brush or comb, and remaining broken hairs will appear frayed at their ends. Hair breakage often results from multiple insults to the hair shaft over time, and damage to healthy hair does not occur with conventional hair care products. However, certain styling techniques involving the frequent application of heat (with use of a blow dryer, flat iron, or hot comb, for example), bleaching of the hair, and chemical straighteners can all contribute to breakage over time. Luckily the hair follicle itself is not permanently harmed, and once the causative practices are stopped and the damaged hair cut off, the new hair will grow normally.
In addition to breakage, repeated pulling of hair can result in hair loss from the root. This condition, called traction alopecia, typically causes hair loss at the scalp periphery, either in the front (see photo), or over the ears, and sometimes across the back of the neck, depending on where the pull is greatest. While reversible at first, if the damaging activity persists this type of loss can become permanent.
Sometimes hair loss results in round or oval bald patches, as opposed to uniform loss all over. This type of loss has several causes, depending on the hair loss pattern and examination of the scalp surface. Bald patches can be due to a fungal infection, an autoimmune disease called alopecia areata (see photos), or a destructive process to the hair follicle. This latter group of diseases is called scarring or cicatricial alopecia (see photos), because inflammation around the hair follicle eventually results in its permanent destruction. Treatment for a fungal infection requires oral anti-fungal medication. Alopecia areata is treated with topical and injected steroids and oral medications for severe disease. The different types of scarring alopecia are treated with topical and injected steroids, antibiotics, and other oral medications depending on the type of inflammation present.