All of my interaction with salicylic acid has been through Neutrogena’s T-Sal psoriasis shampoo.  I have found that my scalp tends to feel a lot better when I intersperse this shampoo with my usually coal tar / standard shampoo rotation.

Salicylic acid doesn’t treat psoriasis directly so much as it cleanses skin that is affected by psoriasis.  Besides scalp shampoos, salicylic acid is used widely as an exfoliant.   The fact that it is the active ingredient for “warming” facewashes should ring a bell — it is the acidic quality of this compound that deep cleans the skin and clears off all that dead skin and dirt build up.  It also deep cleans and disinfects pores.  It can also be used as an anti-dandruff medication.

Salicylic acid acts as a helping hand for other treatments that have a more direct effect on the psoriasis itself, such as coal tar and other chemical compounds that are continually being developed (Neutrogena’s variation on coal tar, for example, is ‘Neutar’).  After it clears out dead skin build-up, then other medications can have more of a direct access to affect skin cells.

I tend to think that coal tar itself (via shampoos such as Neutrogena’s T-Gel) creates a build-up on my scalp.  This is my hypothesis / observation, partially based on the fact that coal tar is a derivative of a fossil fuel and fossil fuels are inherently dirty.   Also, when I use T-Sal, this residual build-up feeling that develops over time as I use coal tar shampoos goes away immediately — at such times it feels like my scalp can breath freely again.

I would like to verify this suspicion with a dermatologist one of these days.

In any case, I prefer to mix salicylic shampoo into my topical treatment rotation to keep the psoriasis guessing, clean off any residual dead skin on my scalp and to make sure my skin isn’t getting too accustomed to coal tar treatment (and thus immune) which seems to be possible over time judging by my own experience.

I’ll have to ask a dermatologist one of these days whether or not this coal tar build-up hypothesis is true as well.