Understanding Hair Loss - the Basics

What Is Hair Loss?

Hair grows everywhere on the human body except on the palms of our hands and the soles of our feet, but many hairs are so fine they're virtually invisible. Hair is made up of a protein called keratin (the same protein in nails) produced in hair follicles in the outer layer of skin; as follicles produce new hair cells, old cells are being pushed out through the surface of the skin at the rate of about six inches a year. The hair you can see is actually a string of dead keratin cells. The average adult head has about 100,000 to 150,000 hairs and loses up to 100 of them a day; so finding a few stray hairs on your hairbrush is not necessarily cause for alarm.

At any one time, about 90% of the hair on a person's scalp is growing. Each follicle has its own life cycle that can be influenced by age, disease, and a wide variety of other factors. This life cycle is divided into three phases:

• Anagen -- active hair growth. Lasts between two to six years.
• Catagen -- transitional. Lasts two to three weeks.
• Telogen -- resting phase. At the end of the resting phase (two to three months) the hair is shed and a new hair replaces it and the growing cycle starts again.

As people age, their rate of hair growth slows.

There are many types of hair loss, also called alopecia:

Gradual thinning of hair with age is a natural condition known as involutional alopecia. More and more hair follicles go into a telogen, or resting, phase, and the remaining hairs become shorter and fewer in number.

Androgenic alopecia is another form of hair loss. It's a genetically predisposed condition that can affect both men and women. Men with this condition can begin suffering hair loss as early as their teens or early 20s, while most women don't experience noticeable thinning until their 40s or later.

In men, the condition is also called male pattern baldness. It's characterized by a receding hairline and gradual disappearance of hair from the crown. In women, androgenic alopecia is referred to as female pattern baldness. Women with the condition experience a general thinning over the entire scalp, with the most extensive hair loss at the crown.

Patchy hair loss in children and young adults, often sudden in onset, is known as alopecia areata. This condition may result in complete baldness, but in about 90% of cases the hair returns, usually within a few years.

With alopecia universalis, all body hair falls out.

Tearing out one's own hair, a psychological disorder known as trichotillomania, is seen most frequently in children.

Telogen effluvium is hair thinning over the scalp or other parts of the body that occurs because of changes in the growth cycle of hair. A large number of hairs enter the resting phase at the same time, causing shedding and subsequent thinning.