Hair Shedding and Thinning: Why It Happens

Normal shedding and when it is more than normal

It is normal to lose hair every day. The NHS says people can lose between 50 and 100 hairs a day, often without noticing, and MedlinePlus says up to 100 scalp hairs a day is normal and most grow back. [1][2] Hair loss is usually not a sign of something dangerous but can be upsetting, and occasionally it signals a medical condition. [1]

"Shedding" (more hair than usual coming out, often all over the scalp) and "thinning" (less density, sometimes in a pattern) have different usual causes. This page explains the main ones. Evidence labels: established recommendation, promising but limited, mixed, insufficient evidence.

Telogen effluvium (sudden diffuse shedding)

Telogen effluvium is a common cause of diffuse hair loss without scarring, usually set off by physical stress such as childbirth or sudden weight loss. [3] It often resolves, but it can be worrying, and a review notes it can be hard to diagnose because many things can trigger it, and there are no targeted treatments. [3] The NHS lists temporary causes of hair loss as illness, stress, cancer treatment, weight loss and iron deficiency. [1] For these, the NHS says hair loss caused by a medical condition usually stops or grows back after recovery. [1]

Other causes

• Pattern hair loss usually runs in families and is a permanent type of hair loss. See Pattern hair loss. [1]
• Medicines and conditions: MedlinePlus lists thyroid problems, diabetes, lupus, certain medicines, chemotherapy, a low-protein diet and poor nutrition. [2]
• Patchy loss may be alopecia areata or a scarring condition. See Alopecia areata and scarring hair loss.
• Hairstyling: tight styling practices have been implicated as risk factors for traction alopecia. [4] See Hair care practices and breakage.
• Nutrition: see Nutrition for skin and hair; testing comes before supplements.

Which tests may a clinician consider

The NHS says a GP can often tell the cause by looking at the hair and scalp. [1] Any further tests depend on your history and are a clinician's decision. Biotin supplements can distort some lab results (see Collagen, biotin and beauty supplements), so mention any supplements.

What you can do

The NHS advises seeing a GP to find out the cause before going to a commercial hair clinic. [1] No treatment is 100% effective, and the NHS notes that finasteride and minoxidil do not work for everyone and only work while used. [1] Wigs, micropigmentation and counseling are options if hair loss is distressing, and support groups exist. [1]

When to get help

See a clinician if you are worried, if hair comes out in patches, if the scalp is red, scaly, painful or scarred, if shedding is sudden and heavy, or if it comes with other symptoms. The NHS says to see a GP if you are worried about hair loss. [1] Patchy loss can be an immune condition, [5] and scarring types cause permanent loss. [6] Read Skin and hair safety and, for iron or thyroid questions, Anemia and iron deficiency.