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Types of Hair Loss

Male Pattern Baldness
Male pattern baldness (MPB) is principally caused by two main factors - possibly assisted by some other more minor ones. The two factors are: 

Presence of a substance called Dihydrotestosterone (DHT) in the vicinity of the hair roots. This substance is produced from the male hormone testosterone by the action of a particular enzyme called 5-alpha reductase. 

Inherited genetic information. 
When a man inherits the necessary gene for some of his hair roots to become susceptible to attack by DHT he will lose hair. MPB therefore has nothing to do with the amount of male hormone a man has - merely the fact that he has any at all is enough to cause the hair loss provided he has also inherited the necessary genetic detail.  Only those hair roots which have been programmed will be attacked by DHT. Normally these will be somewhere through the top region of the scalp with at least those hair roots around the sides and back of the scalp not being susceptible to attack by DHT. Hence, many men are left with a ‘monks fringe’ of hair at the sides and back. The chart below outlines the normal progression of male pattern baldness:

Female Hair Loss
Perhaps surprisingly there is a strong connection between male pattern baldness (MPB) and the typical hair loss patterns seen in females.  As well as having the necessary enzyme (5-alpha reductase) capable of forming DHT from the male hormone testosterone (everyone has both male and female hormones) a woman also has an enzyme called aromatise which converts some male hormone into a female type. This has the effect that much of the hair loss which would have occurred is reversed or prevented by the counterbalancing effect of this ‘extra’ female type hormone in the area of the hair roots. As a result it would be extremely unusual for a female to lose as much hair as, say, her brother, even though she may have inherited similar genetic information. It is important to note that the action of the aromatise enzyme converting male hormone into female is usually confined to specific areas of the scalp. For this reason women will often develop a particular pattern of loss. Commonly this will result in the front hair line being retained whilst thinning occurs through the top region of the scalp.  Another point is that at the menopause a woman’s oestrogen (female hormone) level drops. This increases the chances of the residual male hormone testosterone being converted to DHT and thinning may therefore increase at this time. Typical progression of hair loss in females: