Dryness

Hyaluronic acid

Hyaluronic Acid

Holding many times its weight in water is a beaker result. The human trial we found compared it with a ceramide cream in 20 people with atopic dermatitis, and the two products did not differ.

Panthenol

Panthenol

In a three-week study of 23 people on deliberately damaged skin, the reduction in transepidermal water loss was larger than control (−168.36 vs −123.38 g/m²/h, P = .023). What that control was, the abstract does not say.

Centella asiatica

Centella Asiatica Extract

In a split-face trial of 30 people after laser resurfacing, the side treated with Centella extract gel showed a lower erythema index (coefficient −0.03, P = .046) and better crusting and wound appearance in the first days. Skin biophysics, though, did not differ between the two sides.

Glycerin

Glycerin

In a double-blind crossover study of 51 people with dry skin, the finished emollient reduced transepidermal water loss more than the vehicle and more than the vehicle plus glycerol. Moisturising is the work of a formula, not of one ingredient.

Urea

Urea

5% and 40% are effectively different products. At low concentrations it holds water; at high concentrations it dissolves keratin. A 40% cream beat 12% ammonium lactate at two weeks, and in a 167-person trial of a urea-containing cream the primary endpoint was missed (P = .088) while the other measures were significant.

Gluconolactone (PHA)

Gluconolactone

A 1997 trial put four acids side by side and then challenged the skin. Sites treated with gluconolactone lost significantly less barrier function than vehicle, than untreated skin, and than glycolic acid. And the Korean AHA warning text does not apply to this ingredient.

Lactic acid

Lactic Acid

In a 1983 trial, a 12% lactate lotion, a 5% lactic acid lotion and a plain emollient all three significantly improved xerosis. The difference emerged one to two weeks after treatment stopped. And in the 1996 photodamage trial it beat vehicle on four forearm measures — more than glycolic acid managed in the same trial.

Colloidal oatmeal

An ingredient class — not a single line on an ingredient list

In a double-blind trial of 90 children with atopic dermatitis, an over-the-counter 1% colloidal oatmeal cream was non-inferior to a prescription barrier cream. But all three clinical trials we found came from the company that sells it. And none of them included an untreated arm.

Retinaldehyde

Retinal

In a randomised double-blind trial comparing 0.1% and 0.05% creams in 40 Korean women over 13 weeks, there was no statistically significant difference between the two concentrations. Note what the trial lacks: there was no vehicle arm — everyone applied retinaldehyde. A comparison against applying nothing is not here.

Petrolatum

Petrolatum

A 1997 study proposed using petrolatum as the standard reference substance in irritation testing. And in a 2000 trial comparing 'skin-identical lipids' with pure petrolatum, there was no indication the lipids did better. Recorded here as a case where the expensive ingredient did not beat the cheap one.

Stretch mark creams (pregnancy prevention)

An ingredient class — not a single line on an ingredient list

Ectoine

Ectoin

Two randomised trials exist, both in atopic dermatitis. One beat its vehicle but tested a cream that also contained hyaluronic acid; the other tied with a different active cream. Both ran four weeks.

Licochalcone A

Licochalcone A

In an 80-person randomised, investigator-blinded trial, a moisturiser containing licochalcone A was compared against 0.02% triamcinolone acetonide cream. The steroid improved things faster; the moisturiser did better on redness control and hydration. But it was not licochalcone A alone, there was no vehicle-only arm, and after two weeks everyone moved onto the test moisturiser.

Aloe vera

An ingredient class — not a single line on an ingredient list

In a double-blind trial of 12 skin-graft donor sites, epithelialisation was significantly faster: 11.5 days against 13.67. But in the same trial, pain was not significantly reduced. And we found no trial of aloe for cosmetic outcomes — wrinkles, pigment, elasticity.

Astaxanthin

Astaxanthin

This is swallowed. In the 2018 trial (23 people, 10 weeks) the threshold for UV redness rose above placebo, but FUJIFILM supplied both the funding and the authors. In the 2014 trial (44 people, 12 weeks) elasticity and water loss improved, but it was given together with collagen hydrolysate. And in that same trial, UV-induced DNA damage did not differ.

Tocopherol (vitamin E)

Tocopherol

In a 1999 double-blind trial that split each surgical scar in half, vitamin E had no effect or actually made things worse in 90% of cases, and 33% developed contact dermatitis. The authors concluded that its use on surgical wounds should be discouraged. In a six-month trial it absorbed into skin readily but left the lesions unchanged.

Ceramides

An ingredient class — not a single line on an ingredient list

In 39 children with atopic dermatitis randomised three ways, a ceramide barrier cream, another prescription cream and an over-the-counter petrolatum ointment did not differ, and the petrolatum was at least 47 times more cost-effective. Applying emollients to newborns to prevent eczema also failed in a Cochrane review.

Collagen

Collagen

The rule of thumb in the skin-penetration literature is 500 daltons. Collagen is hundreds of times larger. That applying it increases collagen in the dermis has not been established in people.

Genistein

Genistein

In two trials of 30 postmenopausal women over 24 weeks, biopsies from the skin in front of the ear showed hyaluronic acid and collagen had risen. But the comparator was estradiol and genistein lost both times, and there was no vehicle-only arm. Neither trial had an endpoint measuring anything visible.

Snail secretion filtrate

Snail Secretion Filtrate

We found one randomised placebo-controlled trial. 66 people over 12 weeks is a decent size, but it tested a serum of snail filtrate with calendula and liquorice root, not snail alone. One endpoint reached significance — inflammatory acne lesions — with a confidence interval running from −65.24 to −2.53. Non-inflammatory lesions, sebum, hydration, water loss, erythema and the users' own satisfaction all showed no difference.