Sudden or patchy loss
Losing 50 to 100 hairs a day is normal, and most people never notice it. Different is a bald patch or strip that appears within a day or two, hair that comes out in clumps when you brush it, or round, smooth patches on the scalp or in a beard. Patchy loss is the classic sign of alopecia areata, in which the immune system attacks hair follicles. It usually begins in children and young adults, it can come and go, and hair can regrow, on its own or with treatment. A dermatologist can confirm it, rule out other causes such as an infection, and explain what may help.
Based on: American Academy of Dermatology; NHS
A sore, itchy, red or scaly scalp
Pattern hair loss is usually painless, so symptoms in the scalp point elsewhere. Scaly bald patches with small black dots, which are broken stubs of hair, or with sores, can be a fungal infection; on the scalp it usually needs prescription tablets and shampoo, not a cream from the shelf. Intense itching, burning and tenderness can mean an infection, and scalp psoriasis can cause temporary hair loss. Most important are the scarring alopecias, in which inflammation destroys follicles for good. Treatment cannot bring back a destroyed follicle, but it can stop further loss, so they are worth catching early.
Based on: American Academy of Dermatology; NHS
Eyebrows, eyelashes and the front hairline
Losing eyebrows, eyelashes or body hair along with scalp hair is worth a visit. Alopecia areata can affect any hair on the body, and thyroid problems can thin hair too. In women, a front hairline that recedes as a band along the forehead and temples, especially with thinning eyebrows, can be frontal fibrosing alopecia. It is usually diagnosed after menopause, though it can start earlier, and between 80 and 95 percent of women diagnosed with it have lost some or all of their eyebrows, often the first sign anyone notices. It destroys follicles as it goes, and treatment works best when started early.
Based on: American Academy of Dermatology
After a new medicine, an illness or childbirth
Heavy shedding a few months after a high fever, an operation, an illness, a large weight loss, a very stressful time, stopping the pill or giving birth is common. After childbirth it usually peaks about four months later, and most women have their usual fullness back by the child's first birthday. This kind of shedding generally settles within six to nine months once the trigger has passed, but it is worth a check if it lasts longer or has no clear cause. Some medicines can cause hair loss. If you suspect one, talk to the doctor who prescribed it rather than stopping it yourself: stopping some medicines abruptly can cause serious problems.
Based on: American Academy of Dermatology
Children and teenagers
Hair loss before 18 deserves a doctor's look rather than a guess from photos, because the common causes differ. Scalp ringworm, a fungal infection passed on through close contact and shared combs or towels, needs prescription treatment. Alopecia areata usually begins young, tight braids and ponytails cause traction loss in children too, and some people pull out their own hair, sometimes without noticing. Too little iron, zinc or protein, and thyroid problems, can thin hair as well. Pattern hair loss can begin in the teens, but in a young person it should be confirmed, not assumed. In girls and women, hair loss with irregular periods, acne or extra facial or body hair can point to a hormone condition such as polycystic ovary syndrome (PCOS), which the NHS now calls PMOS.
Based on: NHS; American Academy of Dermatology
What a visit involves
A dermatologist starts with questions: when the loss began, how fast it came on, and what else has changed in your health or medicines. They look closely at your scalp, often with a dermatoscope, a lit magnifier, and at your nails and any other area with hair loss, and they may gently pull a few hairs to see how they come out. If a disease, a deficiency, a hormone imbalance or an infection is suspected, a blood test or a small scalp biopsy can follow. Dated photos help, so bring them. Slow, even thinning with no other symptoms is common and not an emergency, and it can be followed calmly between visits.
Based on: American Academy of Dermatology