If an itchy, reddish rash occurs after eating tomatoes, this indicates an intolerance to tomatoes, which can have various causes. The itchy rash may contain fluid-filled vesicles, widespread wheals or pustules filled with pus after an additional infection with bacteria. In addition to the skin, these can also increasingly appear on the lining of the mouth or throat. Often there are additional symptoms, such as gastrointestinal complaints as an indication of the underlying cause in connection with food intake. Avoiding the food will help provide complete symptom relief.
Please also read: Rash - These are the diseases behind it
One reason for a tomato rash can be histamine intolerance. Histamine is found in some foods and is also found in large quantities in tomatoes. Since histamine is released as a messenger substance in the course of an allergic reaction in the body, similar symptoms result in the event of an intolerance.
Another cause is a cross allergy. which occurs mainly in connection with pollen allergies. In this case, the body has specific antibodies for pollen allergens which, due to their structural similarity, react with the molecules contained in tomatoes and trigger an allergic reaction.
If you are further interested in allergic rashes, we recommend reading our article on the subject Rash from allergy
A "tomato allergy" is usually not based on an actual allergy to tomatoes. Often it is a histamine intolerance or a cross allergy. In the case of a cross allergy, the body reacts with a classic allergic reaction when it comes into contact with the tomatoes, as antibodies that are actually specific for another allergen, often grass pollen, incorrectly recognize tomato molecules as their allergen and then trigger an allergic reaction.
Further information on the subject can be found on our page for allergy
The allergic reaction to tomatoes as part of a histamine intolerance is due to the high amount of histamine that tomatoes naturally contain. Histamine is an endogenous messenger substance that is increasingly released in an allergic reaction and contributes to the typical symptoms of an allergy, such as. for example swelling, redness, or itching. This explains the use of drugs that reduce the effects of histamine (Antihistamines) can be used to treat allergic complaints. In the case of histamine intolerance, the additional histamine that enters the body through the tomatoes cannot be broken down and an excess of histamine is created, which leads to the symptoms of an allergic reaction.
Learn more at: Tomato allergy
In people with a grass pollen allergy, antibodies are raised against certain components (Antigens) the pollen formed. If, due to their structural similarity, these antibodies also recognize tomato antigens and then trigger an allergic reaction, it is called a cross allergy. If someone suffers from a cross allergy, they are not primarily allergic to tomatoes, but rather suffer the typical symptoms of an allergy as a result of their pollen allergy. Often there are multiple cross-allergies, such as those against apples or peanuts.
Please also read our topic: Allergy to apples
There are a multitude of different foods that can be affected, but not necessarily! Whether this is the case for you personally can either be clarified by means of an allergy test or you will notice the corresponding symptoms based on the reaction after ingestion of the food.
For more information on pollen-related rashes, see having a rash from pollen
In addition to pollen, a latex allergy can also lead to a cross allergy to tomatoes. It is noticeable that, in contrast to direct allergy, the symptoms of cross allergy appear when the food comes into contact with the food for the first time, as there is no prior sensitization of the immune system to the antigen.
If you are further interested in the topic, read below Cross allergy
The diagnosis of histamine intolerance is usually made as a diagnosis of exclusion based on the clinical picture. The repeated occurrence of symptoms after consuming tomatoes or other histamine-containing foods in the absence of any other explanation makes the diagnosis likely. A diet attempt over two weeks, in which food containing histamine is completely avoided, can help to establish the diagnosis, since no symptoms should arise during this time. In addition, the histamine level and the amount of the histamine-degrading enzyme in the blood can be compared before and after the discharge attempt to establish a diagnosis. Unfortunately, since there is no reliable test to make a diagnosis, the diagnosis is wrongly made in many cases because no other reason has been found.
A cross allergy is also determined primarily by observing the symptoms, but an allergy test is always part of the diagnosis to determine the underlying allergy, for example the prick test.
You can find additional information on our page with the topic Testing for a food allergy
In addition to the itchy red rash, there may also be increased burning or redness with itching in the mouth and throat. Headaches and dizziness as well as gastrointestinal complaints such as diarrhea, nausea and vomiting occur in some cases. In addition, there may be deviations in blood pressure in the sense of an increase above normal or a decrease. Joint pain and water retention are also possible. In the case of cross-allergies with pollen, allergic asthma can also manifest itself in the form of severe breathing difficulties.
If swelling occurs in the throat, a doctor should be consulted as soon as possible, as intolerance can lead to life-threatening shortness of breath. A condition with severe circulatory impairment is an urgent indication for a doctor's visit.
Regardless of the planned therapy, the presence of an intolerance should be confirmed by the doctor before beginning.
The easiest way to avoid the recurrence of a rash is to avoid the food that causes it, especially tomatoes in this case. If other foods, for example because of a cross allergy or because of the high histamine content, also lead to the symptoms, these should also be avoided. In the case of histamine intolerance, a low-histamine diet is recommended.
In the acute situation, the symptoms can be alleviated by taking antihistamines. In the case of histamine intolerance, this is also a treatment option if the consumption of foods containing histamine cannot be avoided. Taking diamine oxidase, the enzyme that breaks down histamine, can also provide relief.
If a cross allergy is the cause, desensitization can be attempted. This is a therapy in which the allergen is regularly injected under the skin for a second period of two to four years so that the body gets used to the substance over time. Desensitization is currently the only therapy that is a causal treatment of the allergy.
Further information on potential therapeutic measures for a food allergy can be found under the following link: Therapy for food allergies
Tomato juice rash
Both the cross allergy and the histamine intolerance are not only triggered by raw tomatoes, but can also occur after consuming processed tomatoes (e.g. cooked). Therefore, the consumption of tomato juice, which mostly contains cooked tomatoes, can lead to the allergic symptoms. However, some people react less strongly to cooked tomatoes than to fresh ones. This is very different in individual cases and should therefore be tried out.
Manifestations on the face
The allergic reaction can also lead to swelling and red rashes on the face, with the face and hands generally being particularly often affected in allergic rashes.
In addition, an allergic runny nose, similar to the widespread hay fever, can also occur with increased discharge from the nose.
Read more on the topic: Rash On The Face - What Is The Cause?
Rash around the mouth
The allergic symptoms often occur after eating tomatoes, especially in the area of the oral mucosa. This also affects the lips, so swollen and itchy lips are common. Theoretically, the skin reaction can occur all over the body, but is often observed primarily where there was direct contact with the allergen, in this case the tomatoes.
This rash is not to be confused with the rose in the mouth, which also leads to typical reddening of the skin around the mouth. This is usually triggered by excessive hygiene or excessive use of care products or cosmetics. The rash typically occurs regardless of food intake.
Please also read: Rash around the mouth