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My Fennel Allergy

author image Diane Marks
Diane Marks started her writing career in 2010 and has been in health care administration for more than 30 years. She holds a registered nurse license from Citizens General Hospital School of Nursing, a Bachelor of Arts in health care education from California University of Pennsylvania and a Master of Science in health administration from the University of Pittsburgh.
My Fennel Allergy
Fennel is commonly used as an herbal supplement or a spice. Photo Credit: FrancoDeriu/iStock/Getty Images

Fennel is an herb that has been used as an herbal remedy for various gastrointestinal conditions and as a spice in food. Fennel is also commonly used in natural insect repellents. An allergic reaction to fennel can form from ingesting the herb as a dietary supplement or using the herb topically on the skin. If you develop any adverse reaction while using fennel, call your doctor and discuss your symptoms. In rare cases, fennel could cause anaphylaxis, a severe allergic reaction.

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Ingested Fennel

If you take fennel as an oral supplement, an allergic reaction can transpire internally causing various symptoms. Typically most symptoms develop within minutes of taking a fennel supplement. You may become dizzy, lightheaded and feel faint. Symptoms related to your respiratory system may include difficulty breathing, shortness of breath, wheezing, coughing, sinus congestion, runny nose, postnasal drip and chest tightness. You may develop diarrhea, nausea, vomiting, stomach pain, bloating and gas. Ingesting fennel can also cause skin reactions after it has been ingested.

Topical Fennel

Fennel is used topically as a natural insect repellent and can cause allergic skin reactions. The most common skin reaction from topically applying fennel is allergic contact dermatitis. This condition is a localized allergic reaction that causes inflammation and swelling in the area that has been exposed to the herb. The skin can turn red and become very itchy. Treat this type of skin rash by washing the affected area with soap and water and applying hydrocortisone cream. Stop using fennel on your skin.

Allergy Cause

An allergic reaction to fennel occurs because your immune system doesn’t identify the substance as safe. The body reacts to fennel as if it is an intruding substance and attacks it with immunoglobulin E antibodies. These antibodies cause mast cells to manufacture excessive amounts of histamine. Histamine is the primary chemical that is responsible for most allergy symptoms. Histamine is produced in soft tissue, which causes swelling and inflammation. How much histamine is released will determine the level of severity of your symptoms.


Treatment for a fennel allergy begins with proper identification and a diagnosis. Your doctor will perform allergy tests to confirm and diagnose your condition. Avoidance is most effective way to prevent an allergic reaction. If you accidentally ingest fennel, call your doctor. Minor symptoms, such as a runny nose or wheezing, may be treated with an antihistamine. More severe allergic reactions may require an injection of epinephrine, administered by a medical professional.

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