If you develop a skin rash after eating nightshade vegetables such as potatoes, peppers or tomatoes, you most likely have an allergy to these vegetables. According to the Mayo Clinic, allergy to nightshade vegetables is uncommon. After eating nightshade vegetables, write down any adverse side effects you experience and make an appointment with your doctor. Common skin conditions associated with nightshade vegetables are contact dermatitis, eczema and hives.
During an allergic reaction, the body's immune system malfunctions, mistaking common foods or nontoxic substances as harmful. After eating or touching nightshade vegetables, your body overreacts to substances in the vegetables and begins developing antibodies to fight off the allergen, according to the Mayo Clinic. The presence of these antibodies causes other chemical reactions that lead to inflammation and irritation in soft tissue. Histamine is one chemical that soft tissues produce to help protect the body from harmful substances. Histamine causes inflammation and irritation when it is released throughout the body.
Three types of skin reactions can accompany nightshade vegetable allergy. Contact dermatitis is general inflammation and itching due to direct contact with a nightshade vegetable. Shortly after touching the vegetable, the skin becomes blotchy, inflamed and irritated in response to increased histamine in the skin. Hives may form in various shapes and sizes. Hives are flat on top and have defined borders. This type of skin rash can appear, disappear and reappear for no apparent reason. Hives are commonly safe unless they form in the ear or throat. If you have eczema, an allergic reaction to nightshade vegetables can cause a flare-up, according to the American Academy of Allergy, Asthma and Immunology.
If a food allergy is causing your skin rash, you may experience other food allergy symptoms as well. These symptoms include digestive issues, such as nausea, vomiting, bloating, diarrhea, gas and abdominal pain. Some people experience wheezing, coughing, chest tightness and shortness of breath. Nasal congestion, a runny nose, sneezing and eye irritation may also occur from an allergic reaction to nightshade vegetables.
The American Academy of Allergy, Asthma and Immunology recommends using topical steroid creams to alleviate a skin rash that develops after contact with nightshade vegetables. You can use hydrocortisone for minor allergic skin conditions or ask your doctor for a prescription for corticosteroids if the rash is severe.
The Mayo Clinic recommends using an oral antihistamine to alleviate common allergy symptoms and skin rashes that may develop during an allergic reaction. Older antihistamines, such as diphenhydramine, are stronger and work faster than newer antihistamines, such as loratadine, do.