Limonene

Limonene is a fragrance terpene used at low levels (often <1%) but is a well-recognized contact allergen, especially after oxidation into hydroperoxides, and is a common positive in patch-testing among fragrance-sensitive and eczema-prone patients. While it may not sting everyone immediately, its sensitization and delayed dermatitis risk in compromised skin is clinically meaningful, and cumulative exposure from multiple fragranced products increases the likelihood of reaction. For patient safety—particularly in atopic dermatitis and post-procedure skin—I score it as significant irritation/sensitization potential. Safety Notes: In mainstream leave-on skincare (creams/serums/sunscreens) limonene is typically present only as a trace constituent of added fragrance/essential oils, commonly appearing around ~0.0001–0.05% (often just above EU allergen declaration thresholds). Rinse-off cleansers and fragranced body products can run higher (~0.01–0.5%) due to higher total fragrance loads and shorter contact time. The upper end is observed in consumer-available essential-oil-forward products and citrus oil blends (e.g., facial oils, balms, scrubs) where limonene naturally comprises a large fraction of the oil; depending on the level of citrus oil used, finished products can reach multi-percent limonene, with specialty OTC formulations approaching ~8%.