# How can testosterone cause both hair growth and loss, and are there other effects that switch?

**URL:** <https://boards.straightdope.com/t/how-can-testosterone-cause-both-hair-growth-and-loss-and-are-there-other-effects-that-switch/817222>\
**Category:** Factual Questions\
**Created:** [July 3, 2018, 10:26am UTC](https://boards.straightdope.com/t/how-can-testosterone-cause-both-hair-growth-and-loss-and-are-there-other-effects-that-switch/817222 "2018-07-03T10:26:19Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![squish7](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squish7/32/104_2.png) [@squish7](https://boards.straightdope.com/u/squish7)\
**Post date:** [July 3, 2018, 10:26am UTC](https://boards.straightdope.com/t/how-can-testosterone-cause-both-hair-growth-and-loss-and-are-there-other-effects-that-switch/817222/1 "2018-07-03T10:26:19Z")

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How can testosterone (‘T’) cause both hair growth and hair loss? Type “testosterone hair” in Google and the top two suggestions are:  
testosterone hair loss  
testosterone hair growth  
I’ve read some stuff but I still don’t get it. Nothing seems to mention the _relationship_ between the two. T is a hormone that causes body hair growth at puberty; at what point or factors does T invert and do the _ **opposite** _ of what it originally is for?

I’ve had lifetime low T, and when I take T treatments (e.g. by an endocrinologist’s prescription, or on a supplement like creatine which as a side-effect raises T availability), I notice the effects that T is supposed to have. It’s a little bit like I’m going through a form of puberty again because I never fully got the hormones to begin with. Like I think my singing voice is lowering a little bit, and I think I notice a tiny bit more hair growth.

Hair growth/loss in and of itself is a minor issue, but my bigger question is: **Are there other T effects that will REVERSE themselves at some point?** T affects bone density and muscle mass, THOSE are important. Will T always increase those a man’s whole life, or do those reverse or lessen too??

Thanks for the help as always, guys!

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**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\
**Post date:** [July 3, 2018, 11:35am UTC](https://boards.straightdope.com/t/how-can-testosterone-cause-both-hair-growth-and-loss-and-are-there-other-effects-that-switch/817222/2 "2018-07-03T11:35:02Z")

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It is not really reversal or switch of effects … it is different effects in different locations and at different ages. What happens to pubic hair is not the same as what happens to scalp hair, for example … and both are different than those annoying long ear hairs.

The “how” is because what happens as T (or one of its more potent products, like dihydrotestosterone, DHT) hits receptors and what happens as it hits receptors varies by location and age, and changes in _local_ conversion of T to DHT with age that varies by location.

No idea if there are other changes of the impact of the same level of T that occur with age.