Azelaic acid is a naturally occurring substance that studies have shown to inhibit 5-alpha-reductase in human skin. 5-alpha-reductase converts testosterone into dihydrotestostrone (DHT), accumulation of which in scalp is believed to be responsible for the male pattern hair loss. Inhibition of this enzyme by azelaic acid can reduce the concentration of DHT in scalp and therefore stimulate hair regrowth. Azelaic acid can be found in many prescription acne medications. Azelaic acid is added to minoxidil solutions in hair loss treatment products because it has different mechanism of action in preventing hair loss. Finasteride is a synthetic chemical; it is one of two main hair loss treatments that works by a similar mechanism as azelaic acid.
1. How is Azelaic acid compared to finasteride as a DHT blocker?
It seems that both azelaic acid and finasteride do the same thing. So which one is better? Let's first take a look at the structures of finasteride, testosterone and azelaic acid. Finasteride has similar structure as testosterone (see Figure below). It is a specific competitive inhibitor for type 2 5-alpha reductase that converts testosterone to dihydrotestosterone (DHT). If you have read enough, you will know that high level of DHT in scalp is the cause of male pattern hair loss. So to lower the DHT level in the scalp is the key to reverse hair loss. To convert testosterone into DHT, the reductase has to bind to (or “swallow” to put it in layman's word) testosterone first. When finasteride is present, finasteride will be bound to the enzyme first (because reductase likes finasteride a lot more than testosterone) and block the active site of reductase. As a result, reductase will no longer be able to bind to testosterone and convert it into DHT.
Azelaic acid has drastically different structure from testosterone (see the Figure below). It is a non-specific competitive inhibitor. In other words, 5-alpha reductase is not a big fan of azelaic acid and has no interest in “swallowing” it. However, when the reductase is surrounded by numerous azelaic acid molecules and it will involuntarily and accidentally “swallow” some azelaic acid which will in turn inactivate the enzyme. That is why much higher concentration of azelaic acid is needed compared to finasteride to be effective .
You may have also read somewhere that says Azelaic acid is a both type 1 and 2 5-alpha reductase while finasteride is only a type 2 alpha reductase, and may think azelaic acid is better than finasteride. This is both correct and incorrect. As mentioned above, azelaic acid is a non-specific competitive inhibitor. Neither type 1 nor type 2 alpha reductase likes to swallow it very much. It swallows azelaic acid just because the reductase is all surrounded by azelaic acid and involuntarily intakes it. If the same high concentration of finasteride is used as azelaic acid, it will block the activity of type 1 5-alpha reductase as well. The problem with use of very high concentration of finasteride is the possible side effects. The higher concentration of finasteride you use, the higher chance you may get finasteride side effect. The good news is that clinically studies have showed 1mg of finasteride (0.1% finasteride topical solution) is safe. The chance of having finasteride side effects is almost negligible.
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