Type I Allergy – Causes, Symptoms & Treatment

Type I allergy

Type I allergy is a group of different allergic hypersensitivity reactions of the human body . The classification of the type is based on the classification of Coombs and Gell into four different types. According to the current state of knowledge, this classification is immunologically outdated, but is still maintained and taught in medicine for didactic reasons.

What is Type I Allergy?

The type I reaction is the “classic” allergic reaction, the “immediate type”, in which allergens such as pollen or animal hair trigger the release of messenger substances within seconds to minutes by binding to certain antibodies on so-called mast cells of the mucous membranes.

This then leads to the typical allergic symptoms such as swelling of the mucous membrane, sneezing, itching and reddening of the eyes , asthmatic attacks or, in the worst case, a drop in blood pressure and life-threatening anaphylactic shock reactions .


Such a reaction is usually triggered by large molecules such as pollen, protein, medicines, contrast media or insect venoms. Normally, the body’s reaction to an antigen makes sense because it allows viruses and bacteria to be recognized and fought off as quickly as possible.

In the case of allergies , however, the body’s defense strategy has gotten out of hand: the body reacts to harmless substances as if they were pathogens. To do this, sensitization is first necessary: ​​Nothing major happens when you first come into contact with the antigen. At the cellular level, however, the antigen is recognized as foreign, processed slowly, and the body builds mast cells into its mucous membranes, specialized only to launch an immediate defensive action the next time the same antigen is presented.

If there is a second contact after such a sensitization, these specialized mast cells release massive and completely exaggerated messenger substances, which then trigger the symptoms described at the beginning. In addition to this immediate response, the type I reaction also includes a late response that begins after several hours and can last for days and consists of tissue infiltration with inflammatory cells.

Symptoms, Ailments & Signs

An allergy can trigger various symptoms of varying intensity. These extend either to individual parts of the body or to the entire organism. When an allergy occurs, it usually belongs to type I. A good 90 percent of all cases can be attributed to it. Signs appear immediately, after a few minutes or hours.

The most common complaints concern the skin and the respiratory tract. The skin is red or there is a rash . Wheals often appear . Those affected begin to cough . The swollen mucous membranes ensure that even shortness of breath can set in. Asthma attacks are possible.

The nose, which is also used for breathing, expels liquid mucus. There is a constant urge to sneeze. The allergic reaction sometimes causes the eyes to turn red. An uncontrollable flow of tears sets in. Some patients even feel that their eyes are burning . All of the named symptoms represent a defense reaction of the body.

In addition, general signs can accompany a type I allergy. As a result of the reaction, those affected sometimes complain of sudden tiredness . Headaches and diarrhea can also occur . If the entire organism shows symptoms, caution is advised. Anaphylactic shock is life threatening.

Diagnosis & History

The body ‘s type I allergy can remain localized. This leads to reddening, swelling and the formation of wheals on the skin with itching. If the respiratory tract is affected, as in the case of pollen allergy ( hay fever ), there is a runny nose, sneezing, swelling of the respiratory tract.

If the whole thing happens one floor below, the swelling of the bronchi can also trigger an asthma attack. For example, hay fever can get worse over the years and turn into asthma (“change of floors”).

If the reaction does not take place locally, for example after systemic drug or contrast agent administration, the type I reaction can also take place throughout the body and then primarily affects the bloodstream. Initiated by the released mediators, blood vessels in the whole body are dilated, the blood pools in the legs, is missing in the brain and the affected person becomes unconscious.

This severe reduction in blood pressure leads to a life-threatening lack of oxygen in the brain and internal organs and is referred to as “anaphylactic shock”. It can also occur, for example, if you are stung by a wasp, have an allergic reaction and then faint. Emergency medical treatment is then vital.

The doctor usually recognizes the allergic cause of an emergency based on the history. It is therefore important to be able to give reasonable information about the circumstances under which hay fever, skin reddening, an asthma attack or, in the worst case, fainting occurred.


Type I allergy, the most common type of allergy, is characterized by typical inflammatory reactions immediately after contact with the allergen. In most cases there are no complications. When the allergen contact is ended, the inflammatory reactions usually subside quickly. However, in a few cases, these immune reactions can become so intense that they can even lead to life-threatening complications.

The main complications of type I allergy are allergic asthma and anaphylactic shock. Like other forms of asthma, allergic asthma can become a life-threatening emergency in extreme cases. Severe asthma is characterized by severe shortness of breath, overinflated chest, cyanosis (lips turning bluish from lack of oxygen), exhaustion or even confusion. Cough and tachycardia always occur.

The shortness of breath can become so severe that the patient’s life is in acute danger. Anaphylactic shock is always a life-threatening crisis that requires immediate treatment. It is a circulatory shock caused by massive vasodilatation. The blood pressure drops very sharply and the pulse can hardly be felt.

However, the heart rate increases extremely to compensate. Volume replacement therapy must be performed immediately to save life. Drug therapy can include the use of adrenaline. If possible, the triggering allergen should be removed immediately. Both in allergic asthma and in anaphylaxis, the symptoms subside quickly after the contact with the allergen is interrupted.

When should you go to the doctor?

If you have a type I allergy, you should always see a doctor. Since this disease cannot be healed on its own and the symptoms usually significantly restrict the life of those affected, the disease must always be checked by a doctor. Complete healing is not always possible, although the symptoms can be significantly alleviated. As a rule, the doctor should be contacted if the person concerned suffers from severely reddened skin or if there is a severe rash on the skin. These symptoms usually occur when the person concerned comes into contact with or ingests a certain substance. Burning eyes or breathing difficulties can also indicate a type I allergy.

Type I allergies can be identified relatively easily by a general practitioner or an internist . Further treatment depends on the cause and also on the severity of the symptoms, so that no general prediction is possible.

Treatment & Therapy

There are various therapeutic measures against type I allergies : So-called antihistamines, which prevent the release of the messenger substances involved, can be taken purely symptomatically. This works better for some patients and worse for others.

Emergency sprays, which actively dilate the bronchi after inhalation, help against asthma attacks. This works very well for most asthmatics. In worse emergencies, an emergency doctor always has so-called glucocorticoids with him, such as cortisol , which can be injected into the vein and can slow down the body’s entire defense reaction that has gone out of control.

In addition to these purely symptomatic measures, there is also the long-term option of hyposensitization therapy . Slowly increasing doses of the triggering antigen over a period of months can be used to get the body used to the substance and at the same time wean it off the allergic reaction. This often works well for some allergies such as hay fever, but only rarely for others such as animal hair.


When it comes to prevention, there are various theories: it is certain that every person has a different degree of tendency to allergic type I reactions. If both parents have asthma, the risk of having asthma attacks yourself is significantly higher than in the “normal population”. 10% of all people in Germany have such type I allergies , so the word “normal population” is put in quotation marks here. In children, the proportion is even higher.

At the same time, however, you can do something good for your children if you let them come into contact with dirt: the so-called “hygiene hypothesis” states that children who grew up on farms and played outside a lot develop allergies much less frequently than children from inner city households. Too much hygiene therefore increases the risk of a type I allergy.


The first treatment usually only treats the symptoms of a type I allergy. In many cases, however, targeted follow-up care in the form of hyposensitization or specific immunotherapy (SIT) can be useful. In this way, the allergy is treated in the long term.

As part of the desensitization, the allergy sufferer’s immune system should gradually become accustomed to the substances that are responsible for the occurrence of the type I allergy. So far, hyposensitization has been the only way to counteract the causes of an allergy. With specific immunotherapy, it is possible to improve the symptoms and prevent secondary diseases.

Often, allergy sufferers can even be freed from the symptoms of the allergy in the long term. As a rule, however, it only works in the case of a type I allergy. It must therefore be an immediate-type allergy. During the follow-up care, the allergy sufferer is given the allergen that causes the allergic reactions at regular intervals. The dose increases in the course of treatment.

Specific immunotherapy is divided into an initial phase and maintenance therapy. During the initial phase, the patient is given an injection under the skin with an allergen extract every week. Once the dose is tolerated, maintenance therapy begins, during which the maximum possible dose is injected once a month. As a rule, classical immunotherapy takes up to three years.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.