Haslea Ostrearia Extract

Haslea ostrearia extract is a microalgae-derived antioxidant/skin-conditioning ingredient typically used at low concentrations, and it is not a known primary irritant like acids or retinoids. However, botanical/marine extracts are complex mixtures with variable composition and are a recognized source of occasional irritation or sensitization in eczema-prone and highly reactive patients, even when marketed as “soothing.” Given limited robust clinical patch-test data specific to this extract and the need to err on patient safety, I rate it as mild with occasional sensitivity possible. Safety Notes: Haslea ostrearia extract (often standardized to the blue pigment marennine or sold as a microalgae extract blend) is typically used at very low levels in mass-market leave-on serums/creams (around 0.001–0.1%) for marketing/antioxidant/anti-pollution claims, and at similar or lower levels in rinse-off cleansers where deposition is limited. Higher-strength consumer products (concentrated “blue microalgae” boosters/ampoules and some niche masks/serums) can reach ~1–5% when supplied as a diluted extract solution or glycerin/water carrier, with practical limits driven by color impact, odor, stability, and cost rather than specific regulatory caps.