After receiving a number of questions about whether having Covid-19 could lead to hair loss, we asked Professor Andrew Messenger a few questions...

Could experiencing a severe illness, such as Covid-19, trigger hair loss?

Various physical stresses to the body can trigger a type of hair loss called Telogen Effluvium. These include infections associated with a high fever, such as Covid-19 but not limited to it – hair loss was common in the Spanish flu pandemic of 1918-19, for example. Telogen Effluvium can also be triggered by illnesses associated with weight loss (particularly where the body is using up its stores of protein) trauma, including major surgery, crash dieting and some drugs. In these situations, hair follicles in the growth phase of the hair cycle, known as anagen, are precipitated earlier than normal into the resting phase of the cycle, known as telogen. The telogen hair is retained in the follicle for 2-3 months before being shed so the hair loss that occurs in Telogen Effluvium tends to start 2-3 months after whatever has caused it. The other common cause of Telogen Effluvium is childbirth. It is thought that hair follicles tend to be maintained in anagen during pregnancy. Following childbirth those follicles that would have normally entered telogen during pregnancy do so together leading to increased hair shedding 2-3 months later. Whether severe psychological stress can cause telogen effluvium is uncertain although Albert Kligman, the American dermatologist who first coined the term ‘Telogen Effluvium’ in 1961, describes a convincing case in a prisoner following his conviction for murder (he was subsequently pardoned).  

Which types of hair loss can be triggered after a period of ill-health, including viruses and infections?

Telogen Effluvium is the usual cause of hair loss in this situation. In Telogen Effluvium there is increased daily shedding that occurs diffusely over the scalp leading to increased numbers of hairs on the comb or brush, on the pillow or in the plughole after hair washing. There is usually some loss of hair volume, the ponytail may become noticeably thinner for example, and there may be some thinning of hair over the temples. It is unusual to see thinning elsewhere on the scalp unless the shedding is severe. In the great majority of people hair growth will recover spontaneously over 6-12 months providing the cause is no longer present. There have been occasional suggestions, going back into the 19th Century, that Alopecia Areata may be triggered by infections. The evidence for this idea is weak but not much research has been done to prove or disprove it.

Why do some people experience hair loss after illness?

We really don’t know the biology that underlies hair loss following illness nor why some people are more affected than others. However, hair growth is a very dynamic process that depends on vigorous production of new cells and the manufacture of proteins in the hair follicle, and these processes can be depressed by illnesses of various types. This may be seen in other parts of the body besides hair. For example, the growth of finger and toenails may be transiently impaired by illness leading to a transverse furrow across the nail – so-called ‘Beau’s lines’.

If someone is experiencing hair loss after a period of ill-health, what should they do?

The first issue is diagnosis – this may be obvious, for example increased hair shedding after pregnancy is common and probably does not need input from a health professional unless it is severe or persistent. The health visitor is likely to know about it if you are unsure. Similarly, hair shedding after an illness with a high fever is not unusual. However, if you are unsure of the cause of your hair loss, if it is particularly severe or you have other symptoms, you should seek advice from your GP. If you have had Telogen Effluvium due to an identifiable cause, that has now gone away, your hair should regrow naturally and there is not a lot that can be done to speed things up. Patience is needed - hair grows at around one centimetre a month so it can take several months before new hair is long enough to produce a noticeable increase in hair volume. There is some evidence that iron deficiency, which is common in women of child-bearing age, can reduce hair growth and it may be worth asking your doctor for a blood test to check your iron level, and taking an iron supplement if the level is low. Providing you have a normal well-balanced diet there is no evidence that other supplements, such as vitamins and other minerals, will be helpful.     

Thank you to Professor Andrew Messenger for answering these questions. Andrew is a member of Alopecia UK's Research Committee. You can read more about our Research Committee here.