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Thinning hair – what causes hair loss?

Hair loss

You only have to look at your hairbrush or shower drain to see that we all lose hair on a daily basis. Today, as every day, you will lose about 100 hairs but they are usually replaced by new hair growth at around the same rate. However, when the hair follicles stop replacing the lost hair, you will start to notice thinning hair at one or more places on your head.


There are two main causes of thinning hair; genetic factors and other medical and physical factors. Most cases of thinning hair fall into the first category and, despite what the snake oil sellers would have you believe, there is little that can be done about it.


A large proportion of people experience some degree of hair thinning as they grow older, with some men seeing pattern baldness appearing as early as their late teens.


This article on causes of thinning hair and hair loss is by Kathryn Senior, a freelance journalist who writes health, medical, biological, and pharmaceutical articles for national and international journals, newsletters and web sites. 


Hormones and thinning hair

Thinning hair as a result of genetic predisposition is known as androgenic alopecia. This can affect both men and women, although men will experience thinning hair in specific areas, such as on the crown or as a receding hairline, called pattern baldness, whereas women will tend to have more general thinning.


The process requires three factors to produce thinning hair: the hormone testosterone, genetically high levels of a hormone called 5-alpha reductase, and time for the effects of the process to appear.


5-alpha reductase converts testosterone in the blood stream into dihydrotestosterone (DHT), which starts to shrink the hair follicles. As they reduce in size over time, their growth cycle also reduces, producing weaker, thinner hair. Eventually, the hair follicle will reduce to the size it was when you were born.


Your levels of 5-alpha reductase will vary depending on your family tree – although it is worth remembering that you inherit these traits from both sides, so even if your father kept a full head of hair, you may still inherit thinning hair from your mother’s blood line.


Studies have shown that wider genetic factors, such as race and skin colour, also affect thinning hair. Caucasian males are far more likely to experience thinning hair than oriental or African-American males.

Medical causes of thinning hair

While genetic factors are the main cause of permanently thinning hair, sudden or temporary hair loss can be an indication of a range of medical conditions. In some ways, the hair can be seen as a barometer of overall health.


Conditions that affect the blood flow to the scalp, such as diabetes, can cause hair loss, as can rarer conditions like lupus and polycystic ovaries. Sudden onset of thinning hair should always be checked with your GP.


Dietary causes of thinning hair

The health of your hair follicles depends on a range of nutritional factors, and thinning hair can be a result of poor diet and can be slowed or even reversed by changing what you eat.


Hair follicles need vitamins A, E and B to function properly. Vitamin A is vital for the secretion of sebum to keep the hair moist. Lack of vitamin A can result in dry brittle hair that breaks easily before it is ready to be replaced. Vitamin E is essential for the maintenance of the rich blood supply needed by the follicles for healthy hair growth. Vitamin B complexes are required to keep the hair held firmly in the follicle and for strong, healthy hair growth.


Other dietary deficiencies, including lack of iron and lack of protein can also cause thinning hair, as can an excessive dose of vitamin A. However, it should be remembered that dietary deficiencies usually cause general thinning hair all over the head. Changes in your diet are unlikely to help prevent pattern baldness. 

Physical causes of thinning hair

There are many myths about the physical factors that affect thinning hair. For example, many people believe that brushing hair stimulates blood flow to the scalp and helps prevent thinning hair. In truth, bald areas of the scalp have just as good a blood supply as more hirsute areas.


Similarly, people claim that styling can affect thinning hair, but this is also untrue. Cut hair grows no faster than uncut hair and all but the most vigorous blowing and brushing will have little effect on healthy hair.


In truth, physical factors will only affect thinning hair if there is already a pre-existing problem with re-growth due to shrinking follicles. In this case, anything that damages the hair – such as tight plaits, bleaching, styles that pull the hair tight and tight fitting hats – will accelerate the process of hair loss, with the poor quality replacement causing thinning hair.


Thinning hair – it’s just natural

It is ironic that the very hormone which makes men feel masculine, builds confidence and drives their macho libido, is also responsible for thinning hair which can have the opposite effects, but there is little that can be done to prevent it. The rate at which your hair thins is as much a part of your genetic history as your eye colour.


Kathryn Senior

Profile of the author

Dr Kathryn Senior is an acclaimed medical journalist who has written over 500 feature articles for leading international journals within The Lancet group. As Senior Writer at Freelance Copy she produces high quality scientific and medical content for websites and printed publications for companies and organisations in the health, medical and pharmaceutical sectors.



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