Chemical constituent of many natural fragrant ingredients, notably citrus oils such as lemon (d-limonene) and pine trees or species of the mint family (l-limonene).
Topically, limonene can cause sensitivity and is best avoided. Also, because of its penetration-enhancing effects on skin, it’s particularly important to avoid products that contain limonene plus other skin sensitizers like denatured alcohol.
Like most volatile fragrance components, limonene also has strong antioxidant benefits and has also been shown to calm skin; however, when exposed to air these highly volatile antioxidant compounds oxidize and become capable of sensitizing skin.
Reference for this information:
Food and Chemical Toxicology, July 2015, pages 160-170
British Journal of Dermatology, August 2014, pages 292-297
Anti-inflammatory and Anti-allergy Agents in Medicinal Chemistry, March 2014, pages 29-35
Journal of Toxicology and Environmental Health, 2013, issue 1, pages 17-38
Contact Dermatitis, January 2009, pages 32-40