EDTA—This common additive allows ingredients to penetrate your skin more deeply, but it can also cause irritation. If you have redness or itching, see whether anything in your skincare regimen contains EDTA, and then do a patch test on the inside of your elbow to make sure it isn't giving you contact dermatitis.
Bismuth oxychloride—This ingredient is in mineral makeup and other powders, but it's also a common allergen. Like EDTA, a reaction to bismuth oxychloride is typified by redness and itching, but some people may also experience a breakout. Check your foundation, eye shadow, and powder's ingredients lists for this one.
Isopropyl alcohol—Alcohol is drying, and moisturizer, toner, or foundation with isopropyl alcohol can mess up your skin's moisture barrier and dry it out, irritating it and exacerbating acne.
PABA—Even though many sunscreens now tout themselves as being PABA free, this UV blocker, which is known to be a common allergen, can still be found flying under the radar in lots of foundations and lotions with SPF. Using sunscreen is a must, but when you buy, just be aware that chemical sunscreens can irritate, too. Speaking of which . . .
Octyl methoxycinnamate—Another common sunscreen, this UVB blocker is also in a lot of scar reduction creams. If you're allergic, though, redness and acne are common tipoffs.
Sodium laurel sulfate—Sulfates have been in the news lately for rumored links to cancer. Although those claims were found to be unsubstantiated, it's definitely true that many people have skin reactions to it. If you're experiencing itchy scalp or redness after using body wash or shampoo, try an SLS-free shower routine for a week or so to see if your skin improves.