Cystine-thiamin-containing hair-growth formulation modulates the response to UV radiation in an in vitro model for growth-limiting conditions of human keratinocytes.

•The four P-IC components are essential for keratinocyte metabolism and proliferation.•l-cystine and thiamin are major contributors to these beneficial effects.•A combination of tested compounds (P-IC) shows greater effects than the constituent components alone.•Effects of UV-B irradiation in keratinocytes can be significantly modulated by treatment with P-IC.•P-IC modulation of UV response is most likely to act via metabolic support, not just UV filtering.