Tomatoes are a very popular food worldwide, but some people are allergic to them. And although a tomato allergy is rare, skin rashes are one possible symptom.
Skin rashes from tomatoes can be caused by a contact allergy or an ingested (food) allergy.
Here, learn more about the causes behind these skin rashes, how they're diagnosed and possible treatments.
1. Allergic Contact Dermatitis
A skin rash from tomatoes can be the result of allergic contact dermatitis. This is a condition in which the skin becomes red, itchy and inflamed by coming in direct contact with an allergen, per the Cleveland Clinic.
According to an August 2012 review in Contact Dermatitis, tomatoes and other plants can cause contact dermatitis. When it comes to tomatoes, your skin may be reacting to fragrance compounds, proteins in the pulp or peel or something else.
"Allergic contact dermatitis to tomatoes is exceedingly rare," says dermatologist Deirdre Hooper, MD. "It usually shows up as itchy blisters on a red face and is usually in areas that would have naturally come in contact with tomatoes, like hands and arms while gardening, cooking or eating. Usually, allergic contact dermatitis shows up in 24 to 72 hours after contact with the culprit."
The rash isn't usually life-threatening or contagious — it's just pretty uncomfortable. However, the Cleveland Clinic also reports that although extremely rare, allergic contact dermatitis can overlap with anaphylaxis, which is a life-threatening allergic reaction that can close airways.
So, if you notice a skin rash that develops either out of the blue or every time you touch or eat tomatoes, you should talk to your doctor.
How to Diagnose Contact Dermatitis
The best way to confirm a contact allergy to tomatoes or any other substance is a patch test, according to the Mayo Clinic. An allergist will place a patch on your skin with a small amount of an allergen to see if that's what's bugging your skin.
"l always start with the patient's history, see what was going on when the rash started, how it feels, find out where it is on the body, what makes it better, what makes it worse and if I can come up with a clue that they've come in contact with something unusual or new — especially in the last few days," says Dr. Hooper. "In dermatology, we do patch testing, which is when you put small amounts of substances or chemicals on the skin and leave them for a couple of days to see if there's a reaction. I frequently do patch testing when I just can't figure out exactly what is causing what I think is an allergic contact reaction."
2. Food Allergy
A food allergy is your body's immune system abnormally reacting to a certain type of food (after ingesting it), according to Johns Hopkins Medicine. It mistakenly sees the food as harmful to your health and produces allergic reactions. And a skin rash is one of the several types of allergic reactions you can get from consuming an allergen — in this case, tomatoes.
A small 2013 study in the Journal of Investigational Allergology and Clinical Immunology examined a group of people with a known plant food allergy. It was found that tomato allergy happens from an overreaction to various proteins.
The European Centre for Allergy Research Foundation suggests that people who are allergic to birch pollen may also be at risk of having a reaction to tomatoes, because the allergens are similar.
"Symptoms, among which is a skin rash, usually occur within minutes to two hours of exposure to the culprit food," says the Mayo Clinic's allergy-immunologist Jenny Montejo, MD. "The typical skin rash of an allergic reaction is acute urticaria, also known as hives, that presents as raised wheals surrounded by redness."
And oftentimes, according to the U.S. National Library of Medicine, the rash develops around the mouth area.
Diagnosing a Food Allergy
If a skin rash is accompanied by any other symptoms — like swelling, shortness of breath, gastrointestinal problems or breathing problems — a doctor will start testing for a tomato food allergy.
After initial questioning about your history, foods you eat and symptoms you're presenting, a blood test or skin prick test will most likely be done to see if food-specific antibodies are present, per the American College of Allergy, Asthma & Immunology.
A skin prick test is when a small spot on the arm or back is pricked with a probe containing a tiny amount of the food allergen. These tests — that aren't painful, just itchy — are considered positive if a wheal (a small bump) grows at the site. Keep in mind that neither this test nor a blood test can predict the severity of the allergy.
And in some cases, an allergist may opt to do an oral food challenge. This is when a person is slowly fed the suspected allergen under strict supervision.
How to Treat a Tomato Allergy Rash
There are several things you can do to treat a skin rash caused by tomatoes, according to the Mayo Clinic:
- Avoid tomatoes — the fruit and the plant — temporarily, and then try eating or handling them and see if the rash reappears. This will help you determine if tomatoes are the actual cause.
- Apply anti-itch lotion — like hydrocortisone cream — to the affected area. Calamine lotion can help too.
- Take an over-the-counter antihistamine, such as Benadryl.
- Hold a cool, wet compress over the rash for up to 30 minutes, several times a day.
- Don't scratch the area! Cover it if necessary.
- Take a cool bath with baking soda or an oatmeal-based product in the water.
Not sure if you should go to the doctor or wait it out? The Mayo Clinic also recommends seeing a doctor if:
- You're losing sleep or are distracted from normal activities because the rash has become so uncomfortable.
- The rash spreads suddenly and is painful.
- You're embarrassed by the rash.
- The rash hasn't gotten better within a few weeks.
- The rash is on your face or genitals.
It's important to note that while a skin rash is not life-threatening, it could be accompanied by swelling of the face and mouth, trouble swallowing or breathing, lightheadedness, gastrointestinal problems and anaphylaxis. If these symptoms crop up, seek medical help right away.
Is This an Emergency?
- Cleveland Clinic: "Contact Dermatitis"
- Contact Dermatitis: "Tomato Contact Dermatitis"
- Mayo Clinic: "Allergy Skin Tests"
- Johns Hopkins Medicine: "Food Allergies"
- Journal of Investigational Allergology and Clinical Immunology: "Tomato Allergy: Clinical Features and Usefulness of Current Routinely Available Diagnostic Methods"
- European Centre for Allergy Research Foundation: "The Right Tomato For People With Birch Pollen Allergy"
- U.S. National Library of Medicine: "Food Allergy"
- American College of Allergy, Asthma & Immunology: "Food Allergy Diagnosis"
- Mayo Clinic: "Contact Dermatitis: Diagnosis and Treatment"
- Mayo Clinic: "Contact Dermatitis: Symptoms and Causes"