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I feel *so* pedantic making this comment — please forgive me — but also:
CeraVe may have degraded in quality when they were purchased by L’Oréal and potentially changed the source of the fatty alcohols in their formulation. Fatty alcohols that have been sourced from coconut are more likely to cause skin irritation than those that have been sourced from palm. Plus, retinoids can actually push these fatty alcohols deeper into the pores for the ultimate backfire effect. My source is u/WearingCoats on Reddit, who runs a dermatology practice and does product consulting for drugstore brands. She's another one of my favourite resources; I recommend running a search on her posts if there's something specific you're interested in learning.
In general, you don't want to use a moisturizer that is heavy or occlusive over retinoids. It could make the treatment more effective than intended, which might compromise your moisture barrier and contribute to irritated skin. Cetaphil may work better for you if you're going down that route. I personally own a variety of moisturizers, which I rotate depending on what else I'm using on my face, and the season.
This is a very fine point and nobody asked, but the skin on our neck is considered to be more sensitive than the skin on our faces, and retinoids can be more irritating if applied there. There's prescription stuff you can get, but it may be an unnecessary expense. I mix a few drops of cheap drugstore brand retinol (I think by L'Oréal) with moisturizer and apply it to my neck and chest every other day, and I think it has had a smoothing effect on my skin texture. Though again, let's be real, my only metric here is my own subjective assessment of my appearance.
Niacinamide decreases sebum production, which is great for acne, as well as giving your skin a “mattifying” look... but it can also compound a drying effect. I personally apply a few drops in the morning before my moisturizer, but it's one of those things where if you go too hard, too fast, and throw too many things at your skin at once, you're likely to overwhelm your moisture barrier.
Vitamin C is a can of worms. There are a bunch of different compounds that are all called "vitamin C," including L-ascorbic acid (which can come in a powder form, or suspended in water or oils like squalene and silicone), magnesium or sodium ascorbyl phosphate, ascorbyl glucoside, 3-0 ethyl ascorbic acid, and ascorbyl palmitate. (I don’t have a fantastic memory; I grabbed these out of Skincare Decoded.) Water-based L-ascorbic acid serum in combination with vitamin E and ferulic acid is the classic, patented formula developed by SkinCeuticals, which has the most scientific data to back up its claims. However, it's also ridiculously expensive and the price keeps going up. I personally use Timeless' clone of this formula and buy a new bottle every couple of months or so, but there's no way to tell if it's truly effective short of getting into research equipment and controlled studies.
Some of the vitamin C products are better than others, and some are pretty much rubbish (hi hi, ascorbyl palmitate). L-ascorbic acid is notoriously unstable in water, which is why SkinCeuticals holds the holy grail with their patented formula to stabilize it. Sodium ascorbyl phosphate actually has some promising evidence as an acne treatment, and I really think that it should have been marketed as such instead of a less effective L-AA alternative. There are also less-studied antioxidants you might want to check out, like resveratrol and EUK-134. It's important to pay attention to the concentrations that have been studied in clinical trials because many cosmetics lines underdose (or overdose!) their products and can't really claim that they have scientific evidence behind them. For example, The Ordinary's resveratrol formulation contains double the amount that has been studied, which might be irritating to some people's skin.
I'm also skeptical about hyaluronic acid being the holy grail of humectants, compared to good ol' glycerin, especially given the marketing hype around it. Here's a blog post comparing some of the research surrounding the two. Like @nebuchadnezzar pointed out, molecular weight matters, and HA comes in a variety of different sizes so you don't quite know what you're getting in terms of penetration and effects. As they said, humectants are hygroscopic and more generally hydrophilic, meaning, they grab water molecules around them and bind them to themselves, but the downside is that they're not discerning about where they're getting their water from, pulling water from your skin as well as drawing water from the air. If you’re in a dry environment, this can actually work in the opposite direction of what you want. One trick is to apply humectants over wet skin or in the shower, or mist your face with water (when I’m feeling purely indulgent, I use Mario Badescu’s rosewater spray).
@Vanessa Kosoy, it's hard for me to give a straight answer to your question because there are so many factors to consider in your skincare routine, which is why I think a primer on some of the basic science will lead you to being better equipped to pick the right products for you.
Yeah, glycolic acid is an exfoliant. The retinoid family also promotes cell turnover, but in a different way. You'd be over-exfoliating by using both of them at the same time.
Snail mucin is one of those products that has less evidence behind it, besides its efficacy as a humectant, compared to the claims you'll often see in marketing. Here's a 1-minute video about it.
It's true that just because a research paper was published, it doesn’t mean that the results are that reliable — if you dig into the studies that are cited in ads, you'll often find out they had a very small number of participants, or they only did in vitro testing, or they graded their product based on the participants' feelings, or something like that.
I’d also argue that natural doesn’t necessarily mean better. My favourite example is shea butter — some people have this romantic notion that it needs to come directly from a far-off village, freshly pounded, but the reality is that raw shea butter often contains stray particles that can in fact exacerbate allergic reactions. Refined shea butter is also really cool from a chemistry perspective, like, you can do very neat things with the texture.
This is my first time posting to LessWrong! Thanks for asking such an exciting question!
One of my favourite resources is Chemist Confessions. They have a great book that I would recommend as a primer. They often review studies on their podcast and blog, but I'd probably check out the book first.
Stating the obvious, but is it possible for you to see a dermatologist? They might not be trained extensively on the cosmetics side of things, but they'll be able to get you started with a solid routine.
Also, can we please have more threads like this? I think this is the most women I’ve ever seen in one place on LessWrong, like, ever, and it’s really lovely and fun.