Neurocosmetics or Hype? Psychobiotic Potential of Strain-Specific Cosmeceuticals

<b>Background:</b> There is increasing interest in cosmeceuticals-cosmetic regimes incorporating a specific probiotic or postbiotic strain, fully characterized genetically and phenotypically-which, when topically applied, have the ability to modulate the skin microbiome, exhibit anti-inflammatory properties and improve the overall skin appearance by reducing signs of aging. In addition, claims have been made that emotional and psychological well-being can be improved by neuroactive substances released by the probiotics in cosmeceuticals, acting via the skin-brain axis. However, claims are somewhat generalized and imprecise, and we deemed it important to look more precisely at published research relating to cosmeceuticals. There have been very few research publications on these products, identified as neurocosmetics, and they immediately provoked strong reactions from dermatologists and psychiatrists, mainly with regard to the ethical and safety aspects of their use. <b>Objectives/Method:</b> The present strain-centered literature evaluation aimed to select from peer-reviewed publications referring to cosmeceuticals only those dealing with fully characterized, specific probiotic strains with documented beneficial skin properties. Eligible strains found were subsequently subjected to a secondary search to ascertain whether they also demonstrated clinical, or even experimental, evidence of strain-specific psychobiotic properties. <b>Results:</b> From 33 strain-specific cosmeceuticals identified, only three strains-<i>Lactococcus lactis</i> subsp. <i>cremoris</i> H61, <i>Limosilactobacillus reuteri</i> DSM 17938, and <i>Weizmannia coagulans</i> MTCC 5856-demonstrated reproducible evidence of psychobiotic potential. <b>Conclusions:</b> Current evidence does not support the notion that cosmeceuticals are likely to directly modulate emotional states through topical application, since the coexistence of cosmeceutical and psychobiotic properties within the same probiotic strain seems to be both uncommon and highly strain-specific and therefore of little practical, generalized use.