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 unless its presence in skincare products is minuscule. Also, because of its penetration-enhancing effects on skin, it’s particularly important to avoid products that contain limonene plus other skin sensitizers like alcohol.
Reference for this information:
Journal of Toxicology and Environmental Health, 2013, issue 1, pages 17-38