Neither lavender oil nor tea tree oil can be linked to breast growth in young boys Robert Tisserand Introduction In 2007, a correlation was alleged between commercial products containing lavender and tea tree oils and breast growth in young boys. Three cases were seen in boys aged 4-7, who had all been using such products. In each case, the breast growth reduced to normal parameters within several months of ceasing to use the products. Subsequent laboratory testing showed that both essential oils had estrogen-like properties (Henley et al 2007). In the report, no information was given about any of the product ingredients, and there is scant information on product use. No analysis was carried out to confirm or rule out the presence of essential oil constituents. Case one In the first case, "The patient's mother reported applying a "healing balm" containing lavender oil to his skin starting shortly before the initial presentation." No further details of the product or its use are given, but a healing balm sounds like something that might only be applied to a small area of skin. If so, then it is unlikely that any ingredient could have entered the boy's blood in sufficient concentration to cause gynecomastia within a short time period. Case two In the second case, a styling hair gel was applied to the hair and scalp every morning, along with regular use of a shampoo. Both tea tree oil and lavender oil are cited on the ingredient list of both products. In a subsequent website report, it is claimed that the two hair products used in this case were manufactured by Paul Mitchell®, and that these were analyzed by a competitor. The shampoo was said to contain "very low concentrations" of tea tree oil, and the content in the hair gel was "virtually undetectable". Lavender oil concentration was not checked (Neustaedter 2007). Dermal absorption of fragrance from shampoo application has been estimated to be 80 times less than that from body lotion (Cadby et al 2002) and tea tree oil constituents are poorly absorbed by human skin. In one study, only 3% of the essential oil volume, applied as a 20% concentration in ethanol, was absorbed in a 24 hour period (Cross and Roberts 2006). If the website report is reliable, considering that shampoo is a wash-off product, and that there was only a negligible amount of tea tree oil in the hair gel, tea tree oil can be ruled out as a possible cause of this boy's gynecomastia. However, liberal use of a hair gel rich in lavender oil could result in moderate dermal absorption of lavender oil constituents (Cal 2006).