Guaiazulene

Guaiazulene is a soothing, anti-inflammatory azulene derivative typically used at low concentrations (about 0.01–0.1%) in creams and after-sun or “calming” products. It is generally well tolerated and often included for redness reduction, but there are occasional reports of irritation or contact allergy in highly reactive or eczema-prone skin (especially in leave-on products with multiple botanicals). Given the low typical dose yet non-zero sensitization potential, I score it as gentle but not inert. Safety Notes: In commercial skincare, guaiazulene is frequently used as a color/soothing marker ingredient at trace levels (around 0.0001–0.01%) in creams, serums, and aftershaves where it mainly imparts a light blue tint and marketing story. Many consumer "azulene" soothing products sit in the ~0.01–0.1% range, while the upper end observed in OTC retail products is typically ~0.2% in targeted calming balms/spot products and sensitive-skin leave-ons; higher levels are uncommon due to strong coloration and potential for staining/instability rather than regulatory limits. Rinse-off cleansers generally use the low end of the range because of short contact time and color constraints.