QUOTE(LionQueen @ Dec 21 2006, 06:44 AM)

QUOTE(The_Snow_Queen @ Dec 21 2006, 06:08 AM)

Benzoyl peroxide and salicylic acid can be used together, though my position is slightly controversial. If you're interested I'll explain more. You can use salicylic acid with either treatment as often as twice daily, though you may want to use it only once a day or once every other day until your skin gets used to it. How often you use it ultimately depends on your skin's specific needs.
It's great that you brought this up, because I definitely feel that they can be used together successfully, assuming that both products are well formulated. I think the DKR specifically says not to use SA while on the regimen, but I'm assuming this is because most salicylic products out there are such crap.
Anyway, I'd like to hear more about your position on this. My understanding is that BHAs layered under other products (retinoids, BP) actually help the second product penetrate more deeply into the skin. So long as you are cautious and don't have problems with dryness and irritation, you can actually get some really good synergy going.
First, I'll outline some of the benefits of benzoyl peroxide and salicylic acid:
Benzoyl peroxide is considered to be the most effective over-the-counter disinfectant for fighting the p.acnes bacteria. Not only is it considered to be somewhat gentle (though I know a lot of people experience irritation from the treatment), it also penetrates into the hair follicle to kill the bacteria thriving inside a blemish. And lastly, the p.acnes bacteria do not become resistant to benzoyl peroxide overtime.
Salicylic acid exfoliates both the skin's surface and inside the pore, helping to increase the penetration of other treatments. In addition, salicylic acid has antimicrobial and anti-inflammatory properties, improves barrier function, and helps stimulate collagen production. In short, salicylic acid not only helps fight and prevent clogged pores, but it can improve the overall health and appearance of the skin.
Dan and some dermatologists recommend the avoidance of salicylic acid when applying a benzoyl peroxide product. As I've mentioned before, salicylic acid has gotten a bad reputation for being very harsh because most products which contain it are poorly formulated. Some common irritants salicylic acid products typically contain include alcohol denat, SD alcohol 40, other drying alcohols, witch hazel, menthol, peppermint, eucalyptus, and lemon. It is my belief that most people who say not to use salicylic acid and benzoyl peroxide together are thinking only of the poorly formulated salicylic acid products which dominate the market.
Another reason why some advise against using salicylic acid and benzoyl peroxide together is because both treatments make the skin more sun-sensitive. This should definately be a concern, but users of these treatments shouldn't worry too much if they properly use broad-spectrum SPF 15 or higher sunscreens and are smart about trying to avoid staying in the sun too long. (In case anyone reading this doesn't know, broad spectrum sunscreens adequately protect against both UVA and UVB rays. Sunscreens which are not broad-spectrum protect mainly against UVB rays; they may provide some protection against UVA rays, but not enough. If your sunscreen doesn't contain titanium dioxide, zinc oxide, avobenzone, mexoryl sx, or tinosorb, it does not offer broad-spectrum protection and should be replaced).
I find it odd that Dan recommends the avoidance of salicylic acid products in the DKR when he encourages the use of alpha hydroxy acid products as an optional way to help reduce red marks. They are both chemical exfoliants, and well-formulated salicylic acid products may actually be gentler because of salicylic acid's anti-inflammatory properties.
Anyway, as one can see by the benefits benzoyl peroxide and salicylic acid have that were outlined in the first portion of this post, they can compliment each other in the battle against inflammatory acne. If you don't have inflammatory acne, you may as well not waste your money on benzoyl peroxide products because they work mainly to disinfect, and bacteria isn't a problem for those with non-inflammatory acne.
How often you use benzoyl peroxide and saliylic acid depends on you. You can use salicylic acid as often as twice daily and as little as once every other day, and you can use benzoyl peroxide as often as twice daily and as little as once a day. At what times you apply these treatments depends on your personal preferences and how well your skin reacts. If you experience too much irritation lessen your applications, and if you feel like you aren't getting good enough results or simply wish to see how your skin handles more frequent applications of these treatments, increase your applications.