Microalgae as a Sustainable, Natural-Oriented and Vegan Dermocosmetic Bioactive Ingredient: The Case of Neochloris oleoabundans

“Vegan” and “sustainable” characteristics are strong claim trends behind the development of innovative skincare, fragrances, and makeup products. This created a need in the market for compliant ingredients. To date, there have been no records evidencing the use of the microalgae Neochloris oleoabundans (NA) in dermocosmetics. Therefore, we studied the applicability of such a natural compound in this context. NA was cultivated, and the scavenging activity (SA) of the NA extracts was evaluated. The highest SA was from the aqueous extract (54.8% ± 2.1%), being higher than that of the positive control. Two hydrogels were prepared with 1.0% ammonium acryloyldimethyltaurate/VP copolymer: (1) control gel; and (2) gel with a 1.0% NA aqueous extract. In vivo experiments were performed in healthy male and female volunteers with skin phototypes of II–IV. The stratum corneum (SC) hydration and the transepidermal water loss (TEWL) were measured in the forearm of participants to determine their biocompatibility. This parameter was determined by skin bioengineering measurements, confirming that SC hydration and TEWL were not affected by the samples. The laser Doppler measurements results showed a delayed erythema onset in the sites, where the NA hydrogel was applied. The results confirmed the biocompatibility and the anti-inflammatory activity of an innovative ingredient derived from microalgae suitable for a natural and vegan lifestyle.