Hair grows in three distinct phases and replaces itself over a period of three to 10 years. Your health, diet, psychological state and medications you take can all have an influence on your perceived hair loss. If you are in good physical health, your body should be able to handle the number of hairs you lose daily.
Hair Growth Cycle
Hai's active growth period is called the anagen phase. At any time in the growth cycle, 85 per cent of your hair is in this phase. The length of time your hair grows can range from three to 10 years and is determined by your genetic pattern. Your hair's resting stage is the catagen phase, which lasts three to four months. After leaving the catagen phase, your hair enters the telogen phase. This phase is initiated by new hairs developing and pushing the resting hairs out of the root. Not every hair on your head is in the same phase at the same time. Some hairs will be in the telogen phase while others will be in the anagen phase and still others will be in the catagen phase.
What Controls Hair Growth?
At the most basic level in your body, several molecular substances control the growth phases of your hair. Insulin, a hormone used to control blood sugar, is one of these substances. Androgen--the male hormone--is another factor in hair growth. Some hormones, such as platelet-derived factors and fibroblast growth factors, also control your hair's growth. Some of these substances have a positive effect on your hair growth while others have a negative influence. Other factors influencing your hair growth can include an illness that affects several body systems or the drugs you take. Your diet can also influence your hair's growth.
Number of Hairs Lost a Day
Depending up on the growth stage your hairs are in, you can lose between 50 and 100 hairs on a daily basis. Those hairs you lose are in the telogenic phase. If you have a good number of hairs in the growth (anagen) phase, the loss of these hairs will not affect the appearance of your hair. If you do not have enough hairs in the anagenic phase, you might notice thinning hair.
Some kind of systemic shock can initiate a telogenic phase, causing you to lose hair. These shocks can include a high fever, chronic illness, childbirth, severe psychological stress, major surgery, a crash diet deficient in protein, or underactive or overactive thyroid. Medications that cause a telogenic loss (effluvium) include beta blockers, retinoids, antidepressants, NSAIDs and calcium channel blockers.
Factors Affecting Hair Loss
If you have a high number of hairs in the active growth phase, you will not suffer from overall hair loss even if you are losing a high number of hairs in the telogen phase. Conversely, if you aren't losing very many telogen-phase hairs, but your system isn't replacing those hairs with new anagen-phase hair, hair loss could be noticeable.
You can lose more hairs in late summer and in the fall because your hair is preparing for a heavier growth (your "winter coat"). You tend to lose more hairs on the day you shampoo your hair than on the days you don't shampoo.