The signs of an allergic reaction to pistachios can include respiratory symptoms, such as coughing, sneezing, and itchy eyes. Some people also develop asthma symptoms or hives because of this allergy. An individual may also experience nausea and diarrhea or other gastrointestinal symptoms after eating pistachios. In a severe case, a life-threatening reaction can occur and include chest tightness, breathing difficulties, and swelling of the face and throat.

Among the possible signs of a pistachio allergy are upper-respiratory symptoms. For example, a person who is allergic to these tree nuts could develop itchy eyes and sneezing after consuming them. Some people with this allergy may also notice that their throats itch or that they have the urge to cough. A runny nose and dark circles under the eyes are also common with an allergic reaction to pistachios — the dark circles are typically due to the sinus inflammation the allergy causes. The extent of these and other signs of a pistachio allergy generally depend on the severity of the allergy.

Sometimes the signs of pistachio allergies involve the skin, as some affected people develop hives as a reaction. Hives are itchy, raised bumps that develop on the skin as a result of an allergic reaction. They can appear on any part of the affected person's body and can vary quite a bit in terms of size. A person may develop only a few hives, as in the case of a mild allergic reaction, or he may have numerous hives, as in the case of a more severe reaction. Interestingly, hives can disappear in one area and then come back to the same area or move on to another part of the body.

Another sign of an allergic reaction to pistachios is asthma. If an individual who has asthma also has a pistachio allergy, he may experience an increase in asthma symptoms in response to exposure to the nuts. For example, after eating the nuts, he might have an asthma attack. The signs of an asthma attack can include a tightening in the chest, difficulty breathing, wheezing, or coughing. An attack may also interfere with a person's ability to continue his ordinary activities.

Some people also develop gastrointestinal symptoms as an allergic reaction to pistachios. For instance, cramping and diarrhea may develop after consumption. An allergic individual might also experience nausea and vomiting after eating them.

For some people, the symptoms of an allergic reaction to pistachios are both severe and life threatening. In some people, the reaction includes swelling of the face, mouth, and throat; trouble breathing; and abnormal heart rhythms. This type of reaction may also interfere with normal blood flow through the body. Since these signs can prove fatal, urgent medical attention is warranted.