Stridex "in the red box", manufactured by Blistex, is a cult product that's worthy of the hype - it's cheap ($4.28 for a box of 55 wipes on iHerb, with plenty of juice so you can use it for far longer), and contains a tried-and-true product with multiple benefits: salicylic acid (aka BHA), which is exfoliating, turnover-improving, anti-acne and anti-irritant to boot. But salicylic acid is only really effective at certain pHs and concentrations (more on why this is next week) - so will this actually be as effective as more expensive products?
I have Stridex in both the red and blue packaging.
The red version excitingly labels itself as Maximum, referring to the 2% salicylic acid it contains (2% is the highest allowed for an over the counter skincare product in the US).
The blue version brands itself as Essential with Vitamins. It contains 1% salicylic acid, along with vitamin E (antioxidant) and C (antioxidant, but notoriously unstable so the unsealed jar packaging isn't doing it any favours).
Both tick the box for the recommended concentration (1-2%), but don't have any information on their pH (lower than pH 4 is needed for an effective product at these concentrations).
Red box is at a comfortable pH 3-4
Blue box is at a higher pH of 4-5
(I actually repeated the test with some strips that have a more distinguishable difference between pH 4 and 5, and confirmed the same results.)
Red box: Good concentration? Check! Good pH? Check! Stridex in the red box is ideal if you want maximum salicylic acid action at a bargain price - just look out for irritation and allergic reactions, and if you have sensitive skin, start off slowly (once every three days at first or less).
Blue box: While having a pH slightly out of the recommended range isn't an automatic death knell for HA products (more on this in a later post), combined with the low 1% concentration, we have a product that's unlikely to deliver enough salicylic acid for you to notice any exfoliant or turnover improving benefits. It will still work as a toner that's pH appropriate for skin and will remove any makeup you didn't manage to wash off, but it doesn't really have any other noteworthy skincare benefits. (This tub is Lot 041306, Exp 04/15, in case they ever change the formulation.)
There's also Stridex in green packaging which has 0.5% salicylic acid - I'm not sure about the pH, but since it's branded as "sensitive" I would guess that it's above the recommended pH, and it's on the dilute side, so I doubt the salicylic acid would have much effect. Another option, Natural Control, has 1% salicylic acid, unknown pH.