| Active Ingredient | Uses based on scientific evidence | Grade* |
| tea tree oil (melaleuca alternifolia [maiden & betche cheel)] | early studies have found that tea tree alone or in combination with other agents may be effective against lice. however, large, well-designed trials are still needed before a strong recommendation can be made. | c |
*Key to grades
A: Strong scientific evidence for this use;
B: Good scientific evidence for this use;
C: Unclear scientific evidence for this use;
D: Fair scientific evidence against this use;
F: Strong scientific evidence against this use.