Astaxanthin

Astaxanthin is a carotenoid antioxidant typically used at low concentrations in leave-on products (often ~0.01–0.1%), where it is generally well-tolerated and not inherently exfoliating or pH-dependent. Clinical and consumer safety data suggest a low irritation profile, but as a highly pigmented, lipophilic active it is commonly delivered in oils/solubilizers that can increase stinging or contact reactions in very reactive or eczematous skin. Given the small but real risk of irritation/sensitization in compromised barriers, it fits best as a gentle ingredient rather than very gentle. Safety Notes: In real-world OTC skincare, astaxanthin is most often used at very low levels (about 0.001–0.01%) in leave-on serums/creams due to its intense color, oxidation sensitivity, and typical supply as diluted oil dispersions or encapsulated forms. Higher-strength consumer products (not prescription/pro-only) exist mainly as anhydrous oils/oleogels, ampoules, or encapsulated antioxidant serums where finished-formula astaxanthin can reach ~0.1–0.5% before aesthetic (staining/orange hue) and stability constraints become limiting; rinse-off products are generally at the low end because short contact time reduces the benefit of higher loading.