Thinning hair and losing hair can be a normal part of ageing or may be due to other causes. Age also makes hair become finer.
A person may notice hair loss or thinning when looking in the mirror, such as a widening parting or receding hairline, seeing extra hairs on a comb or brush or changes in how a style such as a ponytail looks.
It is normal to lose around 100 hairs a day, but these usually grow back.
Thinning hair can cause emotional problems. Most hair loss happens without other signs of illness. Seek medical advice if you have concerns.
Some reasons for hair loss cannot be changed, other risk factors may be able to be changed or reduced.
A person's tendency to go bald with male-pattern baldness or female-pattern baldness can be inherited from either parent.
Chemotherapy treatments can cause hair loss and radiotherapy for cancer can make hair fall out in the part of the body where the radiation is directed. Hair loss from chemotherapy is usually temporary. Hair loss from radiotherapy or an operation for cancer may result in hair not always growing back in some places.
Some hair styles, such as ponytails, cornrows, tight plaits or winding hair around heater rollers can cause some hair loss. This is called traction alopecia.
A stressful event can trigger hair loss through hair production being suspended for a period of time. One study found that wives who lost a spouse to death or divorce had a higher risk of experiencing hair loss. Researchers also found smoking, drinking too much alcohol and exposure to sun affected hair loss in men.
Thyroid problems can cause hair to thin or be lost. Hormone changes can also affect the hair and some temporary hair loss can happen after pregnancy.
Some medication can cause hair loss, including anabolic steroids and the blood thinning medication warfarin.
Alopecia areata is a condition causing hair loss, which is thought to be due to problems with the body's immune system.
In scarring alopecia or cicatricial alopecia hair loss, hair follicles are destroyed. This can be caused by other conditions, including lichen planus rash or discoid lupus.
Eating a poor diet is unlikely to cause hair loss. However, iron deficiency anaemia can result in thinning hair.
Hair loss on the feet or legs may be due to circulation problems.
Hair loss is also one symptom in the later stages of cirrhosis or scarring of the liver.
Patchy hair loss is one symptom of the sexually transmitted infection (STI) syphilis. Patchy hair loss is a common symptom of a scalp fungal infection.
Diagnosis of hair loss
If medical advice is sought about hair loss, a doctor or dermatologist may diagnose hair loss by carrying out a physical examination and checking a person's medical history.
Further tests may be arranged, especially if there are other symptoms in addition to hair loss or thinning.
Some hair may be pulled out so hair shafts can be microscopically examined for thickness, length, structure and growth phases.