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Head-to-head evidence comparison — which supplement is right for you?
Sunscreen (SPF) wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Mostly mechanism / observational
Top outcomes
Verdict
Mostly mechanism / observational
Top outcomes
Shared outcomes (1)
Outcomes where both Sunscreen (SPF) and Tretinoin (Retin-A) have evidence — compare verdict strength side-by-side.
Topical OTC. Apply a broad-spectrum SPF 30+ sunscreen daily to sun-exposed skin as the last step of a morning routine, using an adequate amount (about 2 mg/cm² — roughly a nickel-sized dollop for the face, a shot-glass for the body) and reapply every ~2 hours of sun exposure and after swimming/sweating. Mineral (zinc oxide / titanium dioxide) filters are preferred if you're concerned about systemic absorption. There is no oral or systemic dose — it is not ingested. This library does not provide an ingestion protocol.
morning
Broad-spectrum SPF 30+, applied daily; mineral (zinc oxide/titanium dioxide) if concerned about absorption
Prescription topical: a pea-sized amount of 0.025%-0.1% cream or gel applied to clean, dry skin once nightly. Start low-strength and every-other-night to build tolerance. A prescription drug used under clinician direction — not a supplement regimen.
before-bed
Topical cream or gel, 0.025%-0.1% (prescription)
Throughout
Ongoing (years)
Ongoing
Throughout
12-24 weeks
12-24 weeks
Months
8-12 weeks
Sunscreen and prevention of skin aging: a randomized trial.
Ann Intern Med (2013) · Rct · n=903
Randomized community trial (n=903): the daily sunscreen group showed no detectable increase in photoaging (skin microtopography) after 4.5 years
Molecular mechanisms of photoaging and its prevention by retinoic acid: ultraviolet irradiation induces MAP kinase signal transduction cascades that induce Ap-1-regulated matrix metalloproteinases that degrade human skin in vivo.
J Investig Dermatol Symp Proc (1998) · Review
Mechanistic model: UV activates MAP-kinase pathways and AP-1, which upregulate matrix metalloproteinases (MMPs)
Daily Use of a Facial Broad Spectrum Sunscreen Over One-Year Significantly Improves Clinical Evaluation of Photoaging.
Dermatol Surg (2016) · Open label · n=32
Single-arm prospective study (n=32): broad-spectrum SPF 30 applied daily to the face for 52 weeks
Topical tretinoin improves photoaged skin. A double-blind vehicle-controlled study.
JAMA (1988) · Rct
Randomized, double-blind, vehicle-controlled trial of topical tretinoin for photoaged forearm and facial skin
Tretinoin emollient cream: a new therapy for photodamaged skin.
J Am Acad Dermatol (1992) · Rct
Multicenter double-blind vehicle-controlled trial of tretinoin emollient cream for photodamaged skin
Long-term treatment of photoaged human skin with topical retinoic acid improves epidermal cell atypia and thickens the collagen band in papillary dermis.
J Am Acad Dermatol (2005) · Open label
Long-term topical retinoic acid on photoaged human skin assessed histologically
Sunscreen (SPF) has a higher evidence score (9/10 vs 8/10) and wins in 2 of 3 categories.
For reduce wrinkles & fine lines, Sunscreen (SPF) has a higher relevance score (90 vs 80).
No known interactions between Sunscreen (SPF) and Tretinoin (Retin-A) have been documented in our database. However, always consult a healthcare provider before combining supplements.