Extremophiles are microorganisms that populate habitats considered inhospitable from an anthropocentric point of view and are able to tolerate harsh conditions such as high temperatures, extreme pHs, high concentrations of salts, toxic organic substances, and/or heavy metals. These microorganisms have been broadly studied in the last 30 years and represent precious sources of biomolecules and bioprocesses for many biotechnological applications; in this context, scientific efforts have been focused on the employment of extremophilic microbes and their metabolic pathways to develop biomonitoring and bioremediation strategies to face environmental pollution, as well as to improve biorefineries for the conversion of biomasses into various chemical compounds. This review gives an overview on the peculiar metabolic features of certain extremophilic microorganisms, with a main focus on thermophiles, which make them attractive for biotechnological applications in the field of environmental remediation; moreover, it sheds light on updated genetic systems (also those based on the CRISPR-Cas tool), which expand the potentialities of these microorganisms to be genetically manipulated for various biotechnological purposes.

The integration of extremophile-derived bioactives into cosmeceuticals and nutricosmetics offers a novel strategy to enhance skin health through both topical and systemic approaches. Extremophile microorganisms, adapted to extreme conditions, produce unique compounds such as ectoine, extremozymes, carotenoids, exopolysaccharides (EPSs), and mycosporine-like amino acids (MAAs). These molecules exhibit antioxidant, anti-inflammatory, photoprotective, and regenerative properties. This review analyzes the molecular adaptations that enable extremophiles to synthesize these compounds, and explores their cosmetic applications, including enzymatic exfoliation, UV protection, hydration, and anti-pollution effects. This paper examines their nutraceutical potential, highlighting systemic benefits such as improved skin elasticity, reduced photoaging, and modulation of the gut–skin axis via prebiotic EPSs. Industrial strategies for sustainable production, such as microbial fermentation, synthetic biology, and green extraction, are discussed. Examples of commercial ingredients like PlusXanthin™, Antarctic-G, and Desertica. Extremophile-derived ingredients combine biological efficacy with environmental sustainability, positioning them as key assets for next-generation skincare. Future directions include clinical validation, regulatory harmonization, and the development of personalized, microbiome-friendly formulations.