Neem Oil Worst Irritant No known benefits Neem Oil description Neem oil contains a chemical known as nimbidin that gives it a sulfur-like odor and some ability to help control fungus and also work as a pesticide. Neem oil can be a skin irritant and is also poisonous if ingested. Avoid this form of neem and note that the constituents that make the oil a problem for skin aren’t present in the extracts, which is why the extracts are rated differently. Related ingredients: Melia Azadirachta Oil