For how we live.
Short trials show topical hyaluronic acid improves skin hydration and, in low-molecular-weight forms, wrinkle depth. It is a humectant on the surface, not a replacement for the acid skin loses with age.
Topical vitamin C is a real antioxidant that helps skin build collagen. Split-face studies show measurable smoothing, but a systematic review found only seven usable trials, almost all mixing it with other actives.
A split-face melasma trial put niacinamide within reach of prescription hydroquinone with fewer side effects. But much of the anti-ageing evidence comes from the ingredient's own manufacturers.
Topical retinol is the over-the-counter cousin of prescription tretinoin. In the cleanest test of the pure ingredient, three-times-a-week retinol beat its own vehicle on fine wrinkles and built new collagen — slowly.
Red-light masks and panels promise photorejuvenation without lasers or needles. A randomised trial of 136 volunteers backs the collagen claim — but it is one good study, and 'red light' covers very different devices.
A high number does buy measurably more protection — in one real-use trial far fewer people burned on the SPF 100 side. But how much you apply, and whether you reapply, moves the needle more than the label.
In the one randomised trial to test it, adults who used sunscreen daily showed no detectable increase in skin ageing over 4.5 years — 24% less than those who used it as they pleased.
Two ingredients carry most of the real evidence. The rest of the multi-step routine adds cost and, when actives are layered too hard, a damaged skin barrier.
Tretinoin beats its own vehicle in randomised trials — though the vehicle does much of the work. In the few head-to-head trials against over-the-counter retinol, both arms improved and tretinoin irritated more.
Collagen, flavanols and polyphenols beat their comparators on skin elasticity and sun tolerance. The pooled estimates carry heterogeneity of 95% to 98%, and some comparators were low doses of the same ingredient.