As always, if you can't access a paper linked, let me know and I'll upload it locally to my site!

SINCE THE BEGINNING OF TIME, skincare and cosmetics have been a part of an individual's effort to control how others perceive them. Ancient civilizations all over the world have developed skin care and cosmetics, reportedly being well developed for the first time in 3100BC by the Ancient Egyptians, around the time of the political unification of Upper and Lower Egypt. Funny how having a large, prosperous civilization will give individuals the time a resources to focus on non-survival oriented tasks. Sounds a little familiar...

For more information, check out this article published in 2017 about facial cosmetics in Ancient Egypt. Of course, the report was put together by the Faculty of Tourism and Hotels at Minia University, Egypt, so it's almost like they stand to gain something from such an article... but if you're especially interested, I'd encourage you to delve into their cited works and look up other academic articles about the topic! Mad that I don't cite better sources? Good! I encourage you to be skeptical of what you read online, no matter how official or confident the sources seems to be.

So what's the big deal about skincare? Why is this market so easy to exploit? As this 2017 paper-- written by two people with PhDs in dermatological sciences-- says:

The concept of skin care is not well defined. It is a kind of umbrella term covering cleansing, perfuming, changing appearance, changing body odor, protecting and keeping the skin in 'good condition'.

Then it later goes on to state:

The information on skin care procedures is plentiful but little scientifically documented and the number of products available for cleansing, soothing, restoring, reinforcing and protecting is of an almost infinite variety.

Basically, skin care is not well defined (yet as we all know, conflated with status, health, and social value), and not scientifically well-documented even though, as the paper continues to detail, it is backed by claims of new scientific technology in dermatology, and uses terms that "seem scientific". This makes it a market with infinite potential for expansion, backed by a facade of scientific rigor that does not often exist.

Three things to keep in mind

Now for the more practical segment of this article: what should you do? I would of course encourage you to read up on subjects and products yourself, but here are a few tips I can provide.

Understand treatments. What do I mean by that? As a rule of thumb, I try to understand four things about a product before I purchase it.

1. What it actually does, how it does it. Many products will say that they "smooth your skin", or "fight acne", etc. But how do these products actually do it? Yes, benozyl peroxide and salicylic acid are used to get rid of acne that has already formed, but how? Yes, glycolic acid is said to remove hyperpigmentation, but what about it actually does that?
2. Delivery mechanism. Does the delivery mechanism make sense? For example, if an active ingredient needs to remain on the skin to take effect, does it make sense for it to be in a cleanser that you wash off? Considering an emollient because they say it moisturizes your skin? Do you even know the difference between a moisturizer and emollient? Does a product need to foam up to work? Use your brain. Get informed by trustworthy sources (not just some guy online like me) if you don't know something.
3. How you handle the treatment. Apply the scientific method here. Don't throw a bunch of things at your skin. Introduce one new product at a time, wait long enough to observe its effects or lack thereof, and then decide whether or not to keep it in your routine. Do you need three products to keep your skin moisturized, or do you just need one product that is better than all three you're currently using? Is your acne not going away because it's caused by bacteria, and you're using a product that claims to fight bacteria by unclogging pores?
4. Cost. Treatments like laser acne treatments or laser scar removal may not always make sense, given their cost and their efficacy. Maybe you're going through puberty and will continue to get acne until your hormones calm down, so those treatments don't even make sense. Many products are way too expensive for what they actually do. Be smart about this, especially if it's not your money that you're spending.

Be realistic about results. Marketing will get you by telling you that a product will fix your problem right away, or claim to hide a problem until it goes away. You need to investigate these claims. Most likely, if you have dehydrated skin, you will notice a difference fairly quickly when using moisturizers, but reducing oil production won't always work quickly. Resist the urge to buy new products when you feel something else isn't working fast enough or working at all.

Understand the problem. For example, you're supposed to have sebaceous filaments. These are necessary for keeping the skin hydrated. Is the problem that you have sebaceous filaments in the first place, or that you're overproducing oil? Is the problem that you need a new product to manage an issue, or do you need to make another lifestyle change, like your diet or how often you clean your tools, sheets, etc? Are you getting acne because of bacteria? Do you know the causes of acne? Knowing this is crucial to treating the skincare problems that you'd like to address.

A Practical Example

Here is an example of what information I like to gather about active ingredients, and how I decide whether or not to use a product.
Product: CeraVe Renewing SA Cleanser
This is what CeraVe claims it does:

Our salicylic acid cleanser not only exfoliates the skin, but with three essential ceramides, hyaluronic acid and niacinamide it also helps soften and smooth the skin without disrupting its protective barrier.

Ceramides:
This cleanser contains: Ceramide NP, Ceramide AP, and Ceramide EOP, like all other CeraVe products (hence the name of the brand). According to this article from 2005, ceramides are fatty acids found between skin cells (in intercellular spaces). Since fats are hydrophobic, they help to keep in moisture that is already there, and it is well known that ceramides play an essential role in structuring and maintaining the water permeability barrier function of the skin. Skin products like these rely on the ceramides being absorbed into the skin.
According to this chapter of Nanotechnology in Cosmetics from 2017 (section 22.3.1.6):

Due to high molecular weight, percutaneous absorption of ceramides is also a controversial debate. Ceramides are very hard to pass through the layers of the skin; it is suggested that they can traverse through the hair follicles and pores to reach the growing levels of skin.

Additionally, this paper and many more, also detail the questionable claims that ceramides can effectively and evenly permeate the skin, especially if your skin is already healthy. This more recent paper from 2022 (and the previous) suggest that topical ceramides are absorbed, but very locally and shallowly. Perhaps enough to be at least mildly effective.
Hyaluronic Acid:
This 2020 blog article attempts to debunk the mythn that hyaluronic acid allows a huge amount of water molecules to bind to it, as companies claim. I was unable to find academic papers that supported the claim that hyaluronic acid can hold up to 1000x it weight in water, so I'm inclined to agree, though I do believe that water molecules can indeed bind to a hyaluronic acid molecule. According to this 2008 paper, hyaluronic acid is used for The biological functions of HA include "control of tissue hydration and water transport", and according to this article: "the stratum corneum, the outermost and non-viable layer of the skin... is particularly effective at preventing the permeation of hydrophilic molecules... into deeper skin layers". The paper goes on to talk about how HA is used to deliver drugs topically, with success, saying in conclusion that "the inclusion of HA in a topical formulation offers clear and unique potential in the delivery and localization of drugs to the skin". I draw no conclusions about HA allowing the other active ingredients in this cleanser to penetrate the skin, but at least the HA itself is getting somewhere.
Niacinamide:
According to this investigation, niacinamides have been shown to penetrate adequately through the stratum corneum, percutaneously and has show clinical significance. It goes on to say:

Studies have shown that niacinamide has the potential to act as an antioxidant, can improve epidermal barrier function, decrease skin hyperpigmentation, reduce fine lines and wrinkles, decrease redness/blotchiness, decrease skin yellowness (sallowness), and improve skin elasticity.51,52 The mechanisms by which niacinamide provides this array of skin benefits is not completely understood, but the role of niacinamide as a precursor to the NADP family of coenzymes may play a significant role in all of these improvements

It also has been proven that it upregulates the synthesis of ceramides, and that the elevation of ceramides after treatment with niacinamide is associated with an improved barrier function as evidenced by a reduced TEWL (transepidermal water loss, or the water that evaporates through skin due to a water vapor pressure gradient on both sides of the skin barrier. It's used to characterize skin barrier function.) and an increase in the cutaneous resistance to potential harmful topical agents.
Salicylic Acid:
As this article is getting long, here is a paper talking about the efficacy of salicyclic acid as an exfoliator, which in turn allows it to treat acne and surface roughness, and here is a paper talking about delivery systems, which states that "Specifically, SA dissolves the protein that binds dead cells to the surface of the skin, making it easy to slough off the dead skin layer during cleansing. This removal of binding proteins is also the mechanism that unclogs pores and exposes P. acnes to the air, thereby accelerating antibacterial activity", and that "SA should be incorporated in a skin-friendly medium that will deliver it via a water-based acne emulsion in an effective manner to eliminate irritation". According to this page, a few emulsifying ingredients are found in this cleanser.
Takeaway
Basically, I bought this product because of its salicyclic acid and nicinamide. I now live with someone who has really oily skin and acne as a result, and I myself would like my skin to be softer and retain more moisture, so this seemed like a better compromise (before I was using basically the same product without the salicyclic acid). I discussed delivery mechanism above, and how I'm sort of iffy on the other two active ingredients, but you get a lot of product for a good price, for me ~1 year's worth of product for ~16 USD. Since I've used similar products from this brand before, and I've been using it for quite a while now, I can also say that I know that my partner and I handle the cleanser well and that it helps! In the end, though, even if its active ingredients hadn't worked, I would've continued to use it until it ran out, unless it was producing adverse effects. A cleanser just needs to clean your skin, after all.

I hoped this'll help whoever is reading make more informed decisions about the skincare products they purchase! Remember to be informed and think critically... thanks for reading this far!