THE RED, AMBER, GREEN GUIDE TO COMBINING SKINCARE INGREDIENTS

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One of the most common questions I get in my DMs and my comment sections on social media is 'can I use ingredient x with ingredient y in the same routine?' So, today we're answering that question in relation to some of the most popular skincare actives on the market...

This guide is going to be pretty straightforward! 'Red' means two ingredients should not be combined as a general rule of thumb because they counteract one another. There might be scenarios where a brand has formulated some sort of encapsulation system that allows them to combine ingredients with a different pH or that would otherwise cancel one another out, but this post is really about picking up Serum 1 with Active A in it and Serum 2 with Active B in it and if you should use these products together in a routine. 

'Amber' means to proceed with caution, i.e. there's nothing inherently incompatible about the two ingredients and they won't cancel one another out, but they might be a bit too much for your skin. If you have sensitive skin and / or you haven't been acclimatising your skin to actives for years, it's probably best to avoid combining these ingredients in a routine. Instead, you can simply use one in the AM and one in the PM or alternate use of them on different days. I also recommend that if you want to try any of my Amber combinations then ensure you're using a gentler form of each ingredient, which we'll get into later.

'Green' means the ingredients aren't only safe for just about anyone to combine, but they're complimentary and enhance the overall benefit when used together. Just note that I have a few stipulations on some of the ingredients in question!

VITAMIN C (ESPECIALLY PURE FORM) + PEPTIDES (ESPECIALLY COPPER PEPTIDES)

This is where pH comes in, because Vitamin C has an low / acidic pH (its chemical name is Ascorbic Acid) and peptides have a high / alkaline pH. As I'm sure you remember from chemistry class; acidic + alkaline = neutral, so neither ingredient has the environment needed to work effectively. Whilst some Vitamin C derivatives can be formulated at closer-to-neutral pH, pure-form Ascorbic Acid definitely needs to be in an acidic environment to work effectively. And an acidic environment can break peptide chains and render them ineffective. Again, some peptides can be formulated at a closer-to-neutral pH, but copper peptides in particular aren't going to be compatible with Vitamin C.

But what if I want to use Vitamin C and peptides in my routine?

Both of these ingredients are great for a well-ageing routine; Vitamin C can protect the skin from free radical damage and in its pure form, even boost up collagen production (which depletes as we age). Peptides are hydrating, plumping and may also help increase collagen in the skin. So it's no surprise many people want the benefits of both in their routine. I would recommend either using one in your AM routine and the other in your PM routine or use them on alternating mornings. Or, if you'd like a one-step formula, the Bliss Bright Idea Vitamin C + Tripeptide Serum* | £19.95 | full review | is a great all-rounder. I can't seem to find it in stock anywhere at the moment but hopefully it's not gone for good! It combines three peptides with a Vitamin C derivative in a hydrating serum base.

VITAMIN C + BENZOYL PEROXIDE 

This is potentially problematic on two fronts: firstly, this is probably going to irritate your skin, and secondly because benzoyl peroxide can cause oxidisation of Vitamin C, which is an antioxidant. All in all, I think they're best kept apart!

But what if I want to use Vitamin C and benzoyl peroxide in my routine?

Benzoyl peroxide is a powerful anti-acne treatment and Vitamin C can help tackle hyperpigmentation and discolouration, so it makes sense that you might want to use both as part of your routine. I recommend using benzoyl peroxide as part of an evening routine (maybe in Epiduo if you want an all-round acne-fighting treatment) and Vitamin C in the morning, so you can reap antioxidant benefits throughout the day (and also because Vitamin C works synergistically with sunscreen to boost the efficacy of both). Benzoyl peroxide is one of those ingredients that's really not more or less beneficial to use in the AM vs. the PM, so given Vitamin C is best for the day, you can bump it into your nighttime routine.

RETINOIDS + EXFOLIATING ACIDS

This is probably the most common one I get asked about, and it's honestly a bit of a grey area! Acids are acidic and retinoids operate at a similar pH to the skin in its natural state, so there's nothing stopping you from using them together, other than your skin's own tolerance. For that reason, before you ask if you can combine these two, consider why you want to and if you could reap just as many benefits without having them in the same routine.

But what if I want to use retinoids and acids in my routine?

Retinoids (Vitamin A derivatives such as retinol and retinal) are our tried and true class of well-ageing ingredients, so it's no surprise that most people want them in their skincare routine to smooth fine lines, increase collagen production and help with texture and discolouration. Exfoliating acids chemically break up dead skin cells on the surface so are a staple in most skincare routines to increase radiance, help with breakouts, smooth the skin and counteract the slowing down of skin cell turnover as we age. If you're using a prescription-strength retinoid, I'd simply skip use of it one night a week and use an exfoliant on that evening. If not, I'd say you can use your retinoid 3-4 times a week and your acid 2-3 times a week on different nights. If you really want to use them together (not every night, obviously, but let's say you want to use your retinoid every night and throw in your acid 2-3 times a week) then only do this with a retinoid your skin is very used to and happy with and only with a nice, gentle acid (like a PHA or mandelic acid). I don't recommend this for sensitive skin or if you're using a heavy-duty retinoid or a really strong acid like glycolic (especially not if it's at a high concentration).

VITAMIN C + RETINOIDS

This is another combination where there's nothing stopping you with regards to the ingredients being able to work together, but it could be a bit much for your skin. Both ingredients have the potential to cause irritation, so you have to be pretty confident in the products you're using and that your skin has acclimated properly to them before attempting to combine them in the same routine, if that's something you really want to do.

But what if I want to use Vitamin C and retinoids in my routine?

This is one of those ones that's a bit of a no-brainer to me, in all honesty. Vitamin C should be used in the daytime to get the most out of its antioxidants and synergistic-with-sunscreen benefits, and retinoids are destabilised by UV, so should be used at nighttime. Ergo, Vitamin C in the AM and retinoids in the PM just makes sense. I don't recommend combining these two yourself (unless perhaps if it's a retinoid followed by a very gentle oil-based Vitamin C derivative), but if you want to try an evening option that combines to two (maybe because you use a peptide every morning) then try the Strivectin Multi-Action Super C Retinol Brightening and Correcting Serum* | £62 | full review. This takes out the guesswork by combining a stabilised Vitamin C derivative with retinol for a formula that's effective but didn't irritate my skin.

PEPTIDES + CERAMIDES

Now we're moving onto ingredients that pair well together! I like a combination of peptides and ceramides because neither are irritating to the skin and they have some great complimentary benefits. Peptides can hydrate the skin, promote collagen production and even help with skin healing and repair. Ceramides are a fundamental component of your skin's lipid barrier, which is what keeps your skin happy, healthy and free from dryness and irritation. They're both good for well-ageing given ceramide and collagen production slow as we age, they're both good for moisturising the skin and they're both great for overnight repair, which is why I like using this duo as part of my PM routine.

VITAMIN C + NIACINAMIDE

This one has to come with a caveat because there are a lot of really strong niacinamide products on the market that could cause irritation, especially if used with a pure-form Vitamin C. However a gentle niacinamide serum or niacinamide in your moisturiser can work really well alongside Vitamin C. They're both great at tackling discolouration and can protect the skin from free radical damage. If you're not confident in picking the 'right' Vitamin C to go with the 'right' niacinamide then try something like the Summer Fridays CC Me Vitamin C Serum | £65 | full review. This hydrating serum combines several Vitamin C derivatives with niacinamide for a skin-protecting, glow-boosting one-step morning serum.

Do you agree with my RAG rating? Which skincare ingredients do you avoid or enjoy combining?

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