The chemistry behind that sun smell.
UV radiation triggers a cascade of metal-mediated biochemical reactions in skin that produces distinctive volatile compounds. The characteristic "sun smell" emerges from an intricate interplay of oxidative processes.
Different volatile compounds from skin
More effective than glutathione (MT)
Metal increase during UV exposure
Metallothionein orchestrates the UV response.
Metallothionein expression surges within 3 hours of UV exposure, with MT-1 and MT-2 isoforms increasing particularly in basal keratinocytes and melanocytes.
Metal Binding Capacity
MT binds seven zinc ions and additional copper or cadmium ions through its 20 cysteine residues, creating a molecular shield against oxidative damage. MT-null mice show significantly greater UV-induced damage.
The Paradox
Under extreme oxidative stress, when UV-induced reactive oxygen species overwhelm defenses, oxidation of MT's cysteine clusters triggers rapid metal release. The GSSG/GSH ratio controls this process.
Fenton Chemistry
Released zinc, copper, and iron ions become available for catalytic reactions, potentially amplifying oxidative damage and volatile compound generation through Fenton chemistry.
What creates the smell.
Lipid Peroxidation
The primary source of UV-induced volatile compounds. 2-nonenal, with its characteristic "greasy and grassy odor," increases significantly with age and UV exposure, particularly after age 40.
Aldehyde Production
Malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) are major contributors to both cellular damage and volatile emissions. Temperature and UV exposure significantly amplify emissions.
Sulfur Volatiles
Copper catalyzes oxidation of cysteine residues in proteins, producing hydrogen sulfide, methyl mercaptan, and dimethyl sulfide - compounds with potent odors detectable at extremely low concentrations.
Metal ions catalyze the reactions.
The Fenton Reaction: Fe²⁺ + H&sub2;O&sub2; → Fe³⁺ + •OH + OH⁻. These hydroxyl radicals attack organic molecules within nanoseconds, creating cascades of volatile products.
Iron
Drives Fenton chemistry generating hydroxyl radicals. Free iron concentrations can increase 10-100 fold during acute UV exposure.
Copper
Particularly effective at generating sulfur-containing volatiles. The copper-dependent enzyme tyrosinase, central to melanin synthesis, may contribute additional compounds.
Zinc deficiency undermines protection.
MT Expression Drops 50%+
Zinc deficiency reduces metallothionein expression by over 50%, compromising the skin's primary metal-binding and antioxidant defense system.
Cofactor for 300+ Enzymes
Zinc serves as a cofactor for over 300 enzymes and 2000 transcription factors, many involved in UV response pathways.
Anecdotal Body Odor Benefits
Clinical observations suggest zinc supplementation (50-100mg daily) may influence body odor, with anecdotal reports of reduced foot odor within 30 days.
What we still don't know.
No studies have performed real-time volatile analysis during UV exposure while simultaneously monitoring melanogenesis, metal dynamics, and lipid peroxidation. This represents a major gap in understanding the complete mechanism.
Technical challenges in measuring volatile compounds at physiologically relevant concentrations require sophisticated analytical methods like solid-phase microextraction coupled with gas chromatography-mass spectrometry.
Supporting skin's metal-binding network.
Understanding these mechanisms offers practical applications: enhancing metallothionein expression through zinc supplementation could reduce both UV damage and associated odor production, while topical formulations that prevent metal-catalyzed oxidation might minimize volatile formation.