There are more products available now for fighting signs of aging than ever before, and it may seem tempting to layer them on top of each other to reap their benefits all at once. But, in this case, 2 x 2 does not equal 4, meaning that layering active anti-aging ingredients on top of each other does not boost their effects. Here’s an article from NewBeauty.com, which explains this perfectly. 
Could your daily beauty routine be putting your skin at risk? Find
out which ingredients you should never combine to avoid problems down
the road.
Every dermatologist and skin-care professional has their own opinion
when it comes to combining ingredients. Some doctors say strong
ingredients should never be mixed together and should be used solely on
their own, while others disagree, saying it’s safe to use them together
as long as they’re applied at different times of the day. Before you
layer product on top of product, seek out the advice of your
dermatologist or plastic surgeon to reduce your risk of irritation.
Don’t mix vitamin C with:
1. Alphahydroxy Acids (AHAs): Overloading your skin
with too many acid based-ingredients (both vitamin C and AHAs are
acid-based) increases your chances of redness, peeling and irritation.
“Some AHAs even come with instructions to wash it off after a certain
amount of time so that the skin can accommodate and tolerate it,” says
Miami dermatologist Loretta Ciraldo, MD.
2. Copper Peptides: Copper peptides help to
encourage elastin and collagen formation, making it necessary for wound
healing. But when used with vitamin C, the effects of each are cancelled
out, rendering the benefits useless.
3. Retinol: Many experts will say that
super-strength concentrations of vitamin C and retinol shouldn’t be
applied to the skin together, or only with extreme caution, since both
are very powerful and can cause the skin to become dry. However, there
are some topical products that contain both ingredients, but chances are
they contain low concentrations of each, making them safe to use.
Don’t mix retinol with…
1. Benzoyl Peroxide: Retinol and
benzoyl peroxide can ward off acne and prevent the formation of new
blemishes, but when used simultaneously, they can counteract each
other’s benefits. Both are drying, exfoliating, peeling agents, and
when they’re mixed together, they can cause excessive peeling, unwanted
pigment, lasting redness and even blistering and scarring.
2. AHAs: Both retinol and AHAs can help to generate
new collagen, but be careful when using them together. “It’s okay to use
both as long as you are not too sensitive to the combination,” says Dr.
Ciraldo. “Most women with sensitive skin need to alternate, applying
the AHA in the morning and retinol at night for the first few weeks so a
tolerance can be built.” If you’re using either a retinoid or AHA, it’s
essential to use a daily sunscreen as well, since both cause UV
sensitivity.