Did we forget about the muscles? A new look at AGA

It’s well recognized that the “bulge” region of the hair follicle houses hair follicle stem cells and is critically important to normal hair follicle cycling. But the bulge region is also the site where the arrector pili muscle (APM) inserts. To date, it has been thought that the APM does not have any active role in any of the various mechanisms of hair loss and more or less acts as a ‘bystander.’


Now, in new model of androgenetic alopecia, Australian dermatologist Rodney Sinclair and colleagues propose a new model for understanding androgenetic alopecia.  They propose that interactions between the APM and bulge are very important and that the APM, in fact, has a key role in the decision of a hair follicle to ultimately miniaturize.


By observing precisely how miniaturization occurs within follicular units – first in so called ‘secondary’ follicles of the follicular unit that are not attached to the APM and only later in‘primary’ follicles which remain attached to the APM for longer – the authors propose that the APM actually plays a role in maintaining follicular integrity.  The authors propose that by maintaining attachment to the APM, hair follicles are prevented from proceeding down the pathway of  permanent miniaturization.


Comment: Like all models, this proposal sets the stage for further exploration. The APM has perhaps been ignored for too long and may have a more important role than we imagined. 



Sinclair R, Torkamani N and Jones L. Androgenetic alopecia: new insights into the pathogenesis and mechanisms of hair loss.  F1000Res. 2015 Aug 19;4 (F1000 Faculty Rev):585

Dr. Jeff Donovan is a Canadian and US board certified dermatologist specializing exclusively in hair loss. To schedule a consultation, please call the Whistler office at 604.283.1887

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