Hair grows in three different cycles: anagen, catagen, and telogen. About 90% of the hair on the head is in the anagen, or growth phase, which lasts anywhere from 2 to 8 years. The catagen, or transition phase, typically lasts 2 to 3 weeks, during which the hair follicle shrinks. During the telogen cycle, which lasts around 2 to 4 months, the hair rests.
Most people normally shed 50 to 100 hairs a day. This usually doesn’t cause noticeable thinning of scalp hair because new hair is growing in at the same time. Hair loss occurs when this cycle of hair growth and shedding is disrupted or when the hair follicle is destroyed and replaced with scar tissue.
The exact cause of hair loss may not be fully understood, but it is usually related to one or more of the following factors:
- Genetics (e.g. family history)
- Hormonal changes or imbalances (e.g. pregnancy, menopause, birth control pills)
- Medical conditions
- Stress (including after surgery)
- Improper nutrition (vitamin and/or mineral deficiency)
Although hair loss may seem like a more prominent problem in men, women are nearly as likely to lose or have thinning hair.
Common Causes of Hair Loss in Women
1. High Cortisol:
Hair loss is often caused by an imbalance in hormone levels. One of the hormones closely connected with hair loss is cortisol.
Cortisol is a steroid hormone that is normally released in response to events and circumstances such as waking up in the morning, exercising, and acute stress. In its normal function, cortisol regulates a wide range of processes throughout the body including metabolism and immune response. It also has an important role in helping the body respond to stress (i.e. the body’s fight-or-flight response).
However, at sustained high levels, cortisol can be damaging over time. Extended stress leads to extended periods of high cortisol levels. While the adrenal glands are busy making extra cortisol, they make less of the hormones that support healthy hair growth.
2. Low Protein Intake:
Hair loss may occasionally be caused by lack of protein in the diet. When this happens, the body will help save protein by shifting growing hairs into the resting phase. Increased hair shedding can occur two to three months later.
3. Elevated Male Hormones:
- Testosterone: High levels of testosterone has been commonly associated with hair loss. Although women have much lower levels of testosterone than men do, there is enough to potentially cause hair loss, particularly during periods of hormonal change. However, researchers now believe that it is not only amount of circulating testosterone that leads to hair loss, but more significantly the level of dihydrotestosterone (DHT) binding to receptors in scalp follicles.
- Dihydrotestosterone (DHT): Testosterone converts to DHT with the aid of the enzyme 5-alpha reductase, which is held in a hair follicle’s oil glands. In high levels, DHT shrinks hair follicles, decreasing hair’s natural growth cycle and ability to replace itself.
4. Thyroid Issues:
Hair loss may be a sign that thyroid hormones are out of balance. Both hypothyroidism and hyperthyroidism can cause hair to shed. Because hair growth depends on the proper functioning of the thyroid gland, abnormal levels of thyroid hormones can result in hair changes if left untreated. When the thyroid gland is overactive (hyperthyroidism), the hair on your head can become fine, with thinning hair all over the scalp. When the thyroid gland is underactive (hypothyroidism), there can be hair loss, not just on the scalp, but also anywhere on the body. In most cases, the hair will grow back once the thyroid disorder is treated.
5. Low Progesterone:
From the time menses begins until menopause, levels of estrogen and progesterone in women ebb and flow to promote reproduction. At about age 35 to 40, women reach the time of perimenopause. This is when their levels of progesterone and estrogen begin to reduce. Progesterone helps to counterbalance the negative effects of estrogen. When there is not enough progesterone to counterbalance estrogen, one may begin to have symptoms of estrogen dominance, such as hair loss.
6. Iron Deficiency:
Iron deficiency hair loss is caused when the body lacks enough iron to produce hemoglobin in the blood. Hemoglobin carries oxygen for the growth and repair of all body cells including the cells that make up hair follicles.
Temporary hair loss such as iron deficiency hair loss is called telogen effluvium. Telogen effluvium is an abnormality of the hair growth cycle that causes hair that would normally be in the anagen (growth) phase of the hair growth cycle to be prematurely pushed into the telogen (rest) phase, causing hair to shed. Because hair is non-essential, hair growth is one of the first processes to be affected when iron or other nutrient deficiencies occur.
7. Zinc Deficiency:
Zinc is a trace mineral that is needed for many important bodily functions in the body such as building healthy cells, regulating hormones, and aiding in the absorption of other nutrients.
Zinc is available through foods such as beef, pork, shellfish, peanuts, and legumes. Zinc deficiency (or hypozincemia) is a nutrient deficiency precipitated by malnutrition or malabsorption of the element. Deficiency may cause weak, brittle nails, diarrhea, slow healing, and hair loss.
- Mayo Clinic: http://www.mayoclinic.org/diseases-conditions/hair-loss/basics/definition/con-20027666
- You & Your Hormones: http://www.yourhormones.info/Hormones/Cortisol.aspx
- Today’s Dietician: http://www.todaysdietitian.com/newarchives/111609p38.shtml
- WebMD: http://www.webmd.com/skin-problems-and-treatments/hair-loss/hair-loss-causes-women