What causes hair loss?

Dr. Jeanne Morrison, PhD
Family Practitioner

Many people experience hair loss because of heredity or stress. Others lose their hair from the use of chemotherapy or other drugs. You might lose your hair if you have some skin infections or thyroid problems. Pregnant women sometimes notice hair loss or thinning in the months following childbirth. Depending on its cause, hair loss can be temporary or permanent.

If you grew up learning that baldness is caused by vitamin deficiencies, poor scalp circulation or too much hat-wearing, you need to know that all these theories have been disproved.

Also untrue:
  • You can tell if you will lose your hair by looking to your maternal grandfather and uncles.
  • 40-year-old men who have not gone bald, never will.
  • Brushing your hair 100 strokes a day makes your hair healthier.
Experts say baldness, or alopecia, is primarily caused by aging, hormonal changes and family history (on either side - or a combination of these.

Generally, there are two types of hair loss:
  • Anagen effluvium, which is permanent hair loss that was caused by the destruction of hair follicles
  • Telogen effluvium, which is a temporary hair loss because of transitory damage to the follicles
Anagen effluvium generally is caused by internally administered medications, such as chemotherapy agents. The medications poison growing hair follicles. Telogen effluvium is caused by an increased number of hair follicles that enter the resting stage. Some of the most common causes of telogen effluvium include:
  • Physical stress -- such as surgery, illness, anemia or rapid weight change
  • Emotional stress -- including mental illness or the death of a family member Thyroid abnormalities
  • Medications -- including high doses of vitamin A (which can be present in diet supplements), blood pressure medications or gout medications
  • Hormonal changes -- including pregnancy, birth control pills or menopause
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Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
To explain what really happens, Dr. Mehmet Oz, Vice-Chair and Professor of Surgery at Columbia University, has to bust two hair loss myths. First, don't blame your mother. "Half of you is from your dad. Half of you is from your mom. The genes can come from either side," Dr. Oz says. Second, if you cut your hair short, it's not going to grow back faster. "That works for hedges. That is not going to work for us. The hair will grow a half an inch a month. That's the way it grows out."

Dr. Oz says hair loss happens when two hydrogen molecules called DHT (dihydrotestosterone) attach to testosterone. "That poisons the hair follicles and causes them to change from making normal hair to this sort of peach-fuzzy material, which is what going bald is all about," Dr. Oz says.

The amount of hair you lose also has to do with the weather. "Springtime, which is when your testosterone levels are actually at your lowest, is when you lose the least hair," he says.

Men have been desperate to hang onto their hair since the beginning of time, but forget about home remedies like baking soda or lemon. "Desperate men do desperate things," Dr. Oz says. "None of those home remedies, I repeat, none will work."

The only real solutions to hair loss, Dr. Oz says, are medications that block DHT production. "They don't put new hair on your head. They will help prevent the hair that's about to fall out from falling out," he says. "And because of that, since you're already normally growing hair, and hair grows in different cycles, you'll actually sometimes feel like you have more hair on your head."
The most common cause of hair loss in both men and women is genetic and it’s called androgenetic alopecia. Other terms for this include “male pattern balding” and “female pattern hair loss.” In fact, heredity accounts for 95 percent of all the cases of baldness (alopecia) in the United States. In androgenetic alopecia, hormones related to testosterone (also called androgens) cause hair follicles to have a shorter than minimal growth phase, resulting in hair shafts that are abnormally short and thin.

The remaining five percent of baldness cases can be due to a number of things including diet, stress, illness, and/or medications. Specific factors that can cause hair loss:

- Medications, vitamins, or minerals: Medications used to treat high blood pressure, heart problems, depression or gout; chemotherapy or radiation treatment for cancer patients; and in some cases, unusually high levels of vitamin A or low levels of iron or protein. For women, birth control pills can cause hair loss.

- Illness, including thyroid disease, severe infection or flu; even fungus infections, such as ringworm of the scalp. For women, childbirth may cause temporary hair loss as well, due to the changes that take place in the body. In some cases, adults or children may have a condition known as trichotillomania, where there is a compulsion to pull out hair from the scalp, eyebrows, or eyelashes.
Dr. Ellen Marmur, MD
Telogen effluvium, which is temporary, diffuse hair loss, commonly occurs due to stress or physical trauma, and it is often associated with hormonal imbalances. It can happen after having a baby or as a result of an illness, surgery, or emotional turmoil. Hair growth and shedding happen in three phases - the anagen, or growth phase; the catagen, or transition stage; and the telogen or resting phase. A shock to the system can cause these growth cycles to reset at the same time so a much larger number of hairs falls out simultaneously. During pregnancy, your hair gets fuller (like everything else in your body, it is growing at a rapid rate), so it may seem that you are losing more strands than normal six months after giving birth, but the hair is probably simply going back to its normal prepregnancy thickness.

Androgenetic alopecia is progressive hair loss due to hormonal changes such as menopause. It is nonscarring but still very distressing. Hair dissipates in the center, in a Christmas tree pattern, and this happens as hormones wane and the strand caliber reverts to that of weaker, vellus hair. The gradual thinning is similar to that in malepattern baldness (although in men the condition may be more genetic than hormonal. Thyroid problems, certain medications, anemia, psoriasis, and vitamin deficiencies can all contribute to hair loss, or alopecia. It is important to see a dermatologist who can do a workup and test you for any serious health problems that can narrow down the cause. The doctor will do a simple blood test or a punch biopsy of the scalp to establish a diagnosis.

There are also other forms of hair loss, including alopecia areata, an autoimmune disorder in which the immune system attacks the hair follicles, and traction alopecia, when hair falls out from being pulled back too tightly on a regular basis. Harsh hair-straightening treatments (ones using chemicals such as formaldehyde) can make hair fall out too.
Simple Skin Beauty: Every Woman's Guide to a Lifetime of Healthy, Gorgeous Skin

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Simple Skin Beauty: Every Woman's Guide to a Lifetime of Healthy, Gorgeous Skin

What if a leading dermatologist just happened to be your best friend and you could ask her anything? DR. ELLEN MARMUR, a world-renowned New York City dermatologist, answers all your questions with...
Daniel E. Zelac, MD
Mohs Micrographic Surgery

Hair loss can be related to a medical condition, such as low iron or thyroid diseases. In some cases, it can be related to a medication that has been prescribed to treat a medical condition. Correcting the underlying medical condition or modifying the medications being taken can lessen or correct the hair loss. A physical condition, such as an injury, can also contribute to hair loss. In these cases, a surgical correction may be appropriate.

Both men and women experience hair loss as a result of the aging process. The extent, distribution, rate of development and age of onset are all individually determined.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.