Skin

Skin aging: two processes, one organ

Your skin is the largest organ in the body and one of the most honest indicators of biological age. Two distinct processes drive skin aging. Intrinsic aging is the genetic clock: telomere shortening, declining NAD+ levels, accumulating senescent cells, and reduced collagen synthesis that drops roughly 1-1.5% per year after your mid-twenties. Extrinsic aging is the environmental damage layered on top. UV radiation accounts for up to 80% of visible facial aging, but pollution, smoking, poor sleep, and excess sugar all contribute ^[1]. The practical takeaway: the gap between your chronological age and how old your skin looks is largely within your control.

UV protection is the single most effective intervention

No other skin intervention comes close to daily sunscreen. UVA rays penetrate deep into the dermis and break down collagen by activating matrix metalloproteinases (MMPs). UVB rays cause direct DNA damage and sunburn. Both accelerate skin cancer risk. A landmark Australian RCT showed that daily sunscreen users had 24% less skin aging after 4.5 years compared to discretionary users ^[2]. Broad-spectrum SPF 30-50, reapplied every two hours during sun exposure, is the minimum. Mineral filters like zinc oxide avoid the endocrine concerns linked to certain chemical filters like oxybenzone. Don't neglect your hands and neck, which age fast but are often forgotten.

Retinoids: the most studied topical for skin aging

Retinoids are vitamin A derivatives and the best-researched anti-aging topicals available. Tretinoin (prescription retinoic acid) at 0.025-0.1% accelerates cell turnover, stimulates collagen I and III production, reduces hyperpigmentation, and thins the stratum corneum while thickening the dermis. A 2025 systematic review and meta-analysis of RCTs confirmed that tretinoin significantly improves fine wrinkles, roughness, and mottled pigmentation in photoaged skin ^[3]. Retinol, the over-the-counter form, converts to retinoic acid in the skin at roughly 10-20x lower potency. It still works, just more slowly. Start with 0.25-0.5% retinol 2-3 nights per week and build up over months to reduce irritation and peeling.

Glycation: sugar damages your collagen

Advanced glycation end products (AGEs) are formed when glucose binds to collagen fibers, creating permanent cross-links that make the protein stiff and brittle. AGE levels in skin collagen increase linearly with age, and high-sugar diets accelerate the process ^[4]. Glycated collagen resists normal breakdown by MMPs, which means your body can't replace damaged fibers with fresh ones. The result is yellowed, less elastic skin. Cooking methods matter too: high-heat techniques like frying and grilling produce more dietary AGEs than steaming or boiling. Reducing sugar intake and choosing lower-temperature cooking methods can slow AGE accumulation.

Supporting skin health from the inside

Collagen peptide supplements (2.5-10g daily) have shown improvements in skin hydration and elasticity in multiple RCTs, though a 2025 meta-analysis noted that independently funded studies show weaker effects than industry-funded ones ^[5]. Vitamin C at 10-20% topically (L-ascorbic acid) and through diet is a required cofactor for collagen synthesis and a strong antioxidant. Omega-3 fatty acids reduce UV-induced inflammation and support the skin's lipid barrier.

Sleep matters more than most people realize. During deep sleep, growth hormone secretion peaks and cortisol drops, creating optimal conditions for skin cell turnover and collagen production. Chronic sleep deprivation raises cortisol, which directly breaks down collagen and elastin ^[6]. The gut-skin axis adds another layer: gut dysbiosis can drive systemic inflammation that shows up as accelerated skin aging, and probiotic supplementation has shown modest benefits for skin hydration and barrier function in early trials ^[7].

Barrier maintenance basics

A healthy skin barrier prevents water loss and blocks pathogens. Ceramide-based moisturizers replenish the lipid matrix. Niacinamide (vitamin B3) at 2-5% supports ceramide production and reduces redness. Over-cleansing with harsh surfactants strips natural oils and disrupts the skin's slightly acidic pH of 4.5-5.5, which is optimal for microbiome balance. Limit chemical exfoliation to 1-3 times per week.

Hormones and skin aging

Estrogen directly stimulates collagen and hyaluronic acid production in the skin. Women lose up to 30% of their skin collagen in the first five years after menopause ^[8]. This hormonal decline explains why skin aging often accelerates dramatically in perimenopause. Hormone replacement therapy can partially reverse this collagen loss, but the decision involves weighing broader health risks and benefits beyond skin alone.