What SPF should you use daily for UV protection?

Use broad-spectrum SPF 30 minimum; SPF 50+ for extended outdoor time. Reapply every 2 hours or after sweating or swimming.

Does SPF rating protect against UVA aging?

SPF measures UVB sunburn protection. UVA protection requires broad-spectrum labeling, PA rating, or critical wavelength ≥370 nm.

Why use tinted sunscreen for melasma?

Tinted formulas with iron oxides block high-energy visible (violet-blue) light that worsens melasma and post-inflammatory hyperpigmentation—clear SPF often leaves this band unfiltered.

12 Hallmarks of Aging

UV protection

UV protection blocks UVA, UVB, and high-energy visible light that drive DNA damage, photoaging, and skin cancer—daily broad-spectrum SPF 30+ is the baseline defense.

Key facts

UV protection blocks UVA, UVB, and high-energy visible light that drive DNA damage, photoaging, and skin cancer—daily broad-spectrum SPF 30+ is the baseline defense.

What SPF should you use daily for UV protection?: Use broad-spectrum SPF 30 minimum; SPF 50+ for extended outdoor time. Reapply every 2 hours or after sweating or swimming.
Does SPF rating protect against UVA aging?: SPF measures UVB sunburn protection. UVA protection requires broad-spectrum labeling, PA rating, or critical wavelength ≥370 nm.
Why use tinted sunscreen for melasma?: Tinted formulas with iron oxides block high-energy visible (violet-blue) light that worsens melasma and post-inflammatory hyperpigmentation—clear SPF often leaves this band unfiltered.

Cumulative exposure across UV and visible bands is a major exogenous source of DNA damage, pigmentation disorders, immunosuppression, and matrix breakdown in skin. Photoaging and keratinocyte carcinogenesis feed back into genomic instability, chronic inflammation, and stem-cell niche damage—upstream of several hallmarks.

UVA (320–400 nm)

Roughly 95% of ground-level UV is UVA. It penetrates the epidermis and dermis (including window glass), making it the dominant driver of photoaging: collagen and elastin breakdown, wrinkling, and persistent pigment darkening. UVA generates reactive oxygen species (ROS) that oxidize DNA bases and lipids, and it can degrade vitamin A in skin. It also suppresses local immune surveillance—relevant to both aging and carcinogenesis. Tanning (including from beds) is largely a UVA response.

UVB (280–320 nm)

UVB is largely absorbed in the epidermis and is the main cause of sunburn (erythema). It is the most efficient band for forming cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts—direct DNA lesions that drive keratinocyte cancers if repair or apoptosis fails. UVB also stimulates melanin production (tanning) and vitamin D synthesis in the skin. SPF ratings primarily reflect UVB protection; high SPF without broad-spectrum UVA coverage leaves major aging and cancer pathways exposed.

UVC (100–280 nm)

UVC is the most biologically aggressive UV band per photon, but stratospheric ozone absorbs almost all of it before it reaches Earth's surface under normal conditions. Routine sun-exposure risk is negligible outdoors. Artificial UVC sources (some germicidal lamps, welding arcs, damaged ozone-era scenarios) can cause severe acute burns and eye injury—avoid direct skin or eye exposure and follow device safety labels.

Violet & blue — HEV (400–500 nm)

High-energy visible (HEV) light sits at the UV border and penetrates into the dermis. In melanin-rich skin it can deepen melasma and post-inflammatory hyperpigmentation through melanocyte and opsin-mediated pathways that standard UV filters do not fully address. Clear mineral and chemical sunscreens may leave substantial HEV transmission; tinted formulas with iron oxides are the most practical blockers. Indoor screens and LEDs emit modest HEV, but cumulative outdoor visible exposure usually dominates.