A link between abnormal breast growth in boys and the use of lavender and tea tree oils has been found.
Eight chemicals in the oils have shown to interfere with hormones.
This growth of man boobs in young boys called gynaecomastia is rare and often has no obvious cause according to BBC Health.
These oils are found in soaps, lotions, shampoos, hair-styling products, alternative cleaning products and medical treatments.
The researchers suggested caution when using the oils.
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A growing number of reported cases of male gynaecomastia have coincided with topical exposure to the oils.
After exposure to the products was stopped, the symptoms subsided.
Previous studies also showed lavender and tea tree oil had properties that competed with or hindered the hormones that control male characteristics, which could affect puberty and growth.
Guidelines to using essential oils.