Lanolin
In plain terms
A rich, waxy moisturizer rendered from sheep's wool, prized for sealing in moisture on very dry skin and lips. Its one real drawback is allergy: it is a recognized contact allergen, named allergen of the year for 2023.
What the evidence shows
Lanolin is the waxy grease that coats sheep's wool, refined into one of the most effective occlusive moisturizers there is; it seals water into dry, cracked skin and is a mainstay of lip balms, nipple creams, and heavy ointments. Its safety story is almost entirely about allergy, not toxicity. Lanolin is a recognized contact allergen, and the American Contact Dermatitis Society named it Allergen of the Year for 2023 to raise awareness of it. The reaction is to the free lanolin alcohols in it, and how often it shows up depends on who is tested: in North American patients patch-tested for suspected allergy, roughly two to three percent react to lanolin alcohol, while in the general population the rate is well under one percent. It is more likely to sensitize skin that is already broken or inflamed, which is exactly where these heavy creams get used, so leg ulcers and eczema are where reactions cluster. Beyond allergy it is not a systemic concern, with no hormone or cancer question attached. For most people lanolin is a superb moisturizer; for someone with a lanolin allergy or chronically broken skin, it is one to leave out, and patch testing settles it.
On the label
Listed as lanolin, wool wax, wool grease, or lanolin alcohol, common in lip balms, nipple creams, and thick ointments. If you have had a reaction to it or you are treating broken or eczema-prone skin, this is one to patch test or skip; for intact, very dry skin it is one of the best sealers there is.