*Some people can have allergic skin reactions to fennel. People who are allergic to plants such as celery, carrot, and mugwort are more likely to also be allergic to fennel. Fennel can also make skin extra sensitive to sunlight and make it easier to get a sunburn. Wear sunblock if you are light-skinned.
*Pregnancy and breast-feeding: Not enough is known about the safety of using fennel during pregnancy. It’s best to avoid use.During breast-feeding, fennel is POSSIBLY UNSAFE. It’s been reported that two breast-feeding infants experienced damage to their nervous systems after their mothers drank an herbal tea that contained fennel.
* Fennel contains a chemical, estragole, which has caused liver cancer in laboratory mice.
*Allergy to celery, carrot or mugwort: Fennel might cause an allergic reaction in people who are sensitive to these plants.
*Hormone-sensitive condition such as breast cancer, uterine cancer, ovarian cancer, endometriosis, or uterine fibroids: Fennel might act like estrogen. If you have any condition that might be made worse by exposure to estrogen, don’t use fennel.