You probably know that we recommend applying retinoids at night because sunlight inactivates them—but there’s more to it. Your skin follows its own biological clock circadian rhythm, with distinct daytime and nighttime physiology determining active ingredient response.
1. Circadian Control of Skin Function
Peripheral clock genes (e.g., BMAL1, PER1) in keratinocytes and fibroblasts orchestrate when cells divide, repair DNA damage, and neutralize reactive species. (Fun fact: Your skin’s “clock” runs on roughly a 24.5-hour cycle—slightly longer than your brain’s master clock!)
2. Barrier Permeability Peaks at Night
After dusk, transepidermal water loss rises and tight junctions loosen, increasing permeability. At this time, thicker, oil-rich formulations (low water content, high occlusivity) penetrate more deeply and seal in moisture more effectively. Clean before application.
3. Sebum and pH Are Highest by Day
Sebaceous gland activity surges under daylight—sebum output can be up to 15% higher between 9 AM and 3 PM—raising surface pH toward 6.0–6.5. Choose daytime serums or lotions formulated to absorb at this pH (for instance, lipophilic emulsions or pH-buffered gels) and include sebo-regulatory actives like niacinamide or zinc PCA.
4. Nighttime Repair and Blood Flow
Nocturnal perfusion increases by as much as 40%, delivering oxygen and systemic actives to the dermis. Medical-grade retinoids, peptides, and DNA-repair enzymes capitalize on this window—when repair pathways (e.g., NER, BER) run at their fastest.
5. Tailor Your Moisturizer to the Hour
– Morning: Lightweight, pH-optimized emulsions with mattifying agents and broad-spectrum UV filters.
– Evening: Rich, occlusive balms or creams containing lipophilic antioxidants (e.g., tocopherol esters), ceramides, and retinoids for maximum repair and hydration.
Next time you shop for moisturizer or active treatment, ask: “Is this optimized for my skin’s daytime or nighttime physiology?” Tailoring by hour ensures every molecule lands where and when it works best. We have a regimen that can work best with your personal biologic clock and schedule. Come discuss!
