Skincare Guide: Sorting What Works and Doesn't

Nothing is more important for your skin than the ingredients you apply to it.

Skincare is gaining strength every day, especially in and through social media. It seems that the "more" products we use, the better our routine is (not true, according to dermatologists).

However, there are so many cosmetic products nowadays that our eyes can get lost, and so can our wallets. The real questions to ask ourselves while we are tempted to buy another one are; do I really need it, is it really effective, or am I just going through the fear of missing out?

The truth is that several active ingredients don't really work as advertised. Have you ever bought biotin for hair loss, and your hair keeps falling out? Or an eye contour that promises to erase dark circles, and you still have them after two months of use? It's because they don't really work or only partly. According to human skin studies, let's find out the effectiveness of the most promised and sold ingredients below.

Inflammatory conditions, dry skin, and aging signs

Vitamin C

Also known as ascorbic acid. Promises antioxidant, antiaging (by increasing collagen production), and anti-pigmentary effects.

It is one of the main promotors of collagen formation for aged skin, but it poorly bypasses the epidermis stratum corneum barrier on its own.¹

Effects on skin appearance:

Serum vitamin C (ascorbic acid) is effective in concentrations greater than 20% in improving skin tone uniformity (decreases the amount of melanin) and elasticity, probably because it prevents collagen damage elastin from the sun. Changes in wrinkles and roughness are very slight or negligible.² ³


It also has an antioxidant effect that depends on the concentration, but a minimum of 3% can lightly photoprotect. This effect has been demonstrated by the amount of ultra-weak photon emissions induced by UVA rays, which Vitamin C reduced in human skin trials.

Vitamin E

Like vitamin C, vitamin E, with α-tocopherol the most abundant, promises to be an effective antioxidant and anti-inflammatory. In clinical studies, the administration of vitamin E is predominantly oral and transdermal, and therefore the evidence is linked to those.

There is no scientific evidence to support Vitamin E in cosmetic formulations as an effective ingredient and antioxidant for facial skin.

Some studies evaluate its effectiveness associated with other ingredients,such as vitamin C, so it is improbable to estimate efficacy individually, while others are anecdotal and in laboratory settings. In conclusion, there is no evidence, and no study has shown that it is effective on facial skin.


Niacinamide has shown different effects in vitro, such as repairing UV-induced DNA damage in human melanocytes, promoting ceramides, free fatty acids, cholesterol synthesis, depigmenting effect, and inhibition of P. acnes induced inflammatory responses of human keratinocytes.¹⁰

Still, there is no scientific evidence in human facial skin that supports cosmetic Niacinamide as an effective ingredient in skin repair, sebum reduction, or any improvement of its general appearance.¹¹ ¹² ¹³

Existing studies are anecdotal, either in forearm skin or in vitro, and are not representative or comparable to facial skin.

Coenzyme Q10

Ubiquinone (coenzyme Q10, Q10) is a fat-soluble antioxidant crucial for cellular energy production that declines with age and under the influence of external stress factors in human skin.¹⁴ A deficit of it leads to gradual loss of mitochondrial function, the development of aging-like disease, and a shortened lifespan in laboratory settings.¹⁵

Only one study on human skin showed some antioxidant and repairing effects on stressed dermis. However, the formulation was tested on the forearm skin and is not comparable or even suitable to facial skin, so its efficacy and tolerance have not been proven.¹⁶ ¹⁷ ¹⁸


Caffeine is a bioactive, low-toxicity component widely used in cosmetics for its in vitro antioxidant effects at low concentrations. It is therefore relatively harmless.¹⁹

Its efficacy on human skin was evaluated in association with sunscreens (hence in synergy) in emulsions: Ethylhexyl methoxycinnamate (7.5%), avobenzone (3.0%), and titanium dioxide (5.0%), each with 2.5% caffeine and vehicles, as well as caffeine alone. Tests were performed on the volar forearm. The results showed that caffeine associated with the filters induced a higher SPF value. However, caffeine alone did not cause any effect.²⁰ ²¹ ²²

Aging signs and acne


Tretinoin and retinoic acid are intended to balance the skin's desquamation process, decrease acne, and increase collagen production.

Effects on photoaged skin:

Tretinoin effectively improves coarse wrinkling, fine wrinkles and hyperpigmented spots when used at 0.05% once daily. This concentration is safe for facial skin and tolerable, although it causes redness in some cases.²³

Another possible consequence of sun exposure, melasma, is also treatable with tretinoin at the same concentration.²⁴ ²⁵

Effects on acne:

Tretinoin is highly effective in mild, moderate or severe acne in single therapy (monotherapy), reducing inflammation and scarring based on clinical photographic evidence. The improvement is more evident the more inflamed the lesions are, probably due to its potent anti-inflammatory effect against Propionibacterium acnes.²⁶

Its effectiveness has been extensively tested on human skin.


Retinol (vitamin A) fights the signs of aging through collagen production, inhibition of collagen degradation, angiogenesis, and alteration of melanin synthesis in aging skin.²⁷

In human skin, retinol can improve the signs of photoaging.²⁸ especially blemishes, facial wrinkles, and the skin's overall appearance by between 20 and 30 percent according to comparative photos before and after treatment, with concentrations starting at 0.15% in serum form.²⁹

Retinol and tretinoin are comparable in their effects. According to two comparative studies, both effectively improve the overall appearance of aging and sun-damaged skin.³⁰ ³¹ However, their results differences are minimal (not significant), with retinol slightly more effective.³²

Alpha hydroxy acids

Alpha hydroxy acids (AHAs) are a class of chemical compounds based on organic acids. The most used are lactic acid, citric acid, mandelic acid and glycolic acid. The typical indication of AHA containing products ranges from skin moisturising, over wrinkles reduction to deep chemical peeling.³³

Hydration: Lactic acid works as a moisturizer keeping the skin hydrated by more than 6 hours at 5%.³⁴

Skin thickness, fine lines and wrinkles: Although glycolic acid and lactic acid are the most promising alpha-hydroxy acids, neither provides true anti-aging benefits when used as cosmetics.³⁴ ³⁵ ³⁶ ³⁷

Indeed, effective formulations are dermatologically applied in controlled medical settings, not in home-applied cosmetics due to their high concentrations.³⁸

Hyaluronic acid

Hyaluronic acid (HA) plays a vital role in synthesising extracellular matrix molecules and epidermal cell interaction with the surrounding environment. It is also said to be the ultimate solution for moisture retention of the skin. But as we age, the HA decreases, and by the time we become adults, this amount decreases to five per cent of baseline.³⁹

Many popular HA formulations are made of large molecules that do not reach the dermis (where it is needed). So you've been applying a serum that doesn't get where it should.⁴⁰

However, when the nano-hyaluronic form is applied, it significantly increases skin hydration and firmness relative to baseline, but few or no cosmetic products specify whether it contains nano molecules or not. Still, the most effective way for HA to work and reach the dermis is through mesotherapy (injections).⁴¹


For years, glycerin has been considered a moisturiser, allowing the skin to retain water and reduce roughness and dryness.⁴² Still, glycerin is used more as part of cosmetic formulations, including humectant, denaturant, fragrance ingredient, hair conditioning agent, skin protectant, and skin conditioner.⁴³

Hydration: Glycerin works as a moisturiser in concentrations higher than 10% to improve dryness and flaking only on body skin.⁴⁴ Its efficacy has not been proven on facial skin.

Glycerin does not work as a humectant and does not prevent the skin from losing water during the day, but it improves the skin's mechanical properties and provides hydration.⁴⁵ ⁴⁶ ⁴⁷

Shea butter

Due to its semi-solid characteristics and buttery consistency, Shea butter is known for being an excellent emollient with nourishing and anti-inflammatory properties, according to literature and in vitro studies.⁴⁸

The truth is that there are no clinical studies on facial skin. It can work as a body moisturizer and as an emollient in dermatological diseases such as eczema.⁴⁹ ⁵⁰ ⁵¹