Hair loss (alopecia) can affect just your scalp or your entire body, and it can be temporary or permanent. Anyone can lose hair on their head, but it's more common in men. Baldness typically refers to excessive hair loss from your scalp. Hereditary hair loss with age is the most common cause of baldness. 

Symptoms

Hair loss can appear in many different ways, depending on what's causing it. It can come on suddenly or gradually and affect just your scalp or your whole body.

Signs and symptoms of hair loss may include:

• Gradual thinning on top of head. This is the most common type of hair loss, affecting people as they age. In men, hair often begins to recede at the hairline on the forehead. Women typically have a broadening of the part in their hair. An increasingly common hair loss pattern in older women is a receding hairline (frontal fibrosing alopecia).
• Sudden loosening of hair. A physical or emotional shock can cause hair to loosen. Handfuls of hair may come out when combing or washing your hair or even after gentle tugging. This type of hair loss usually causes overall hair thinning but is temporary.
• Circular or patchy bald spots. Some people lose hair in circular or patchy bald spots on the scalp, beard or eyebrows. 
• Full-body hair loss. Some conditions and medical treatments, such as chemotherapy for cancer, can result in the loss of hair all over your body. The hair usually grows back.
• Patches of scaling that spread over the scalp. This is a sign of ringworm. It may be accompanied by broken hair, redness, swelling and, at times, oozing.

People typically lose 50 to 100 hairs a day. This usually isn't noticeable because new hair is growing in at the same time. Hair loss occurs when new hair doesn't replace the hair that has fallen out.

Hair loss is typically related to one or more of the following factors:

• Family history (heredity). The most common cause of hair loss is a hereditary condition that happens with aging. This condition is called androgenic alopecia, male-pattern baldness and female-pattern baldness. It usually occurs gradually and in predictable patterns — a receding hairline and bald spots in men and thinning hair along the crown of the scalp in women.
• Medications and supplements. Hair loss can be a side effect of certain drugs, such as those used for cancer, arthritis, depression, heart problems, gout and high blood pressure.
• Hairstyles and treatments. Excessive hairstyling or hairstyles that pull your hair tight, such as pigtails or cornrows, can cause a type of hair loss called traction alopecia
• Hormonal changes and medical conditions. A variety of conditions can cause permanent or temporary hair loss, including hormonal changes due to pregnancy, childbirth, menopause and thyroid problems. Medical conditions include alopecia areata and trichotillomania.

Risk factors

A number of factors can increase your risk of hair loss, including:

• A family history of balding on your mother's or father's side
• Age
• Significant weight loss
• Certain medical conditions, such as diabetes and lupus
• Stress
• Poor nutrition

Prevention

Most baldness is caused by genetics (male-pattern baldness and female-pattern baldness). This type of hair loss is not preventable.

These tips may help you avoid preventable types of hair loss:

• Be gentle with your hair. Use a detangler and avoid tugging when brushing and combing, especially when your hair is wet. A wide-toothed comb might help prevent pulling out hair. Avoid harsh treatments such as hot rollers, curling irons, hot-oil treatments and permanents. Limit the tension on hair from styles that use rubber bands, barrettes and braids.
• Ask your doctor about medications and supplements you take that might cause hair loss.
• Protect your hair from sunlight and other sources of ultraviolet light.
• Stop smoking. Some studies show an association between smoking and baldness in men.
• If you're being treated with chemotherapy, ask your doctor about a cooling cap. This cap can reduce your risk of losing hair during chemotherapy.