Allergies – An Overview of the Different Types

Around 30 million German citizens suffer from allergies (e.g. hay fever, asthma, house-dust allergy, Hymenoptera venom allergy, food allergies, neurodermatitis). An allergy develops when the body’s immune system is triggered by harmless foreign substances from the environment (allergens). This results in inflammatory processes. Chronic allergies in particular can significantly impair quality of life. Reliable allergy diagnostics, including identification of the triggering allergen, are essential for appropriate treatment and thus highly beneficial for the ones affected.

• In the case of an immediate-type allergy (Type I allergy; mediated by IgE antibodies), a reaction occurs immediately after contact with the respective allergen. Typical symptoms include itching, swelling, coughing, and similar reactions.
• In contrast, in a Type III allergy, initial symptoms appear only after 6 to 12 hours. Triggers may include flour dust or mould spores in the air, among others. A Type IV allergy is diagnosed when there is a contact allergy or an allergy to medication, with a reaction occurring only after 24 to 72 hours.

In addition, there are other conditions that present allergy-like symptoms but are not classified as true allergies:

• Pseudoallergy
• Titanium implant intolerance

Hymenoptera venom allergy is one of the classic IgE-mediated allergies. Up to 25% of German citizens are affected by an allergy to Hymenoptera venom. The symptoms of an immediate-type reaction range from local redness and swelling at the sting site to severe breathing difficulties and risk of suffocation with stings in the mouth or throat area, up to systemic, sometimes life-threatening anaphylactic reactions. Hymenoptera venom allergy occurs mainly as an allergy to bee or wasp venom. Allergic reactions to bumblebee, hornet, or mosquito stings are less common.

For the treatment of Hymenoptera venom allergy, specific immunotherapy (SIT) is available for patients with systemic reactions. This therapy offers highly effective protection against the occurrence of further anaphylactic reactions. A prerequisite for initiating this effective treatment is the precise identification of the allergen responsible for triggering the anaphylaxis.

Hay fever is an allergy that typically occurs seasonally. During the flowering season, plant pollen in the air triggers allergic reactions in affected individuals on the mucous membranes of the nose, eyes, and/or upper respiratory tract. Since temperatures are rising due to climate change, the pollen season is becoming longer and more intense, which causes the exposure to increase.

Causes and Symptoms of Hay Fever

Hay fever develops when the body becomes hypersensitive to certain normally harmless allergens such as pollen. After initial contact, the immune system produces IgE antibodies against the allergen, which sensitise specific immune cells (mast cells, basophils) by binding to their receptors. Upon subsequent contact, allergen molecules activate these immune cells via IgE, causing them to release histamine. This messenger substance triggers the typical allergic inflammatory reactions.

The most common symptoms of hay fever primarily affect the eyes and upper respiratory tract. When allergenic pollen reaches the nasal mucosa, affected individuals experience sneezing, a runny or blocked nose – this is known as allergic rhinitis. If the eyes are also affected, the condition is called allergic rhinoconjunctivitis. Additional symptoms such as itching and asthmatic complaints may also occur.

The most common symptoms include:

• Red, watery, itchy eyes
• Sneezing
• Runny nose
• Swollen eyelids
• Nasal congestion
• Swelling around the mouth/airways

In terms of overall wellbeing, symptoms such as fatigue, sleep disturbances, and exhaustion often accompany rhinitis or rhinoconjunctivitis. Since certain food allergens are related to pollen allergens, individuals with hay fever may also react to certain foods due to the structural similarity of the allergens. This phenomenon is known as cross-allergy.

Allergic bronchial asthma also belongs to the most common forms of allergy. Bronchial asthma is a chronic inflammatory disease of the airways characterised by sudden, reversible narrowing of the bronchi (bronchial obstruction). The cause is a hypersensitive bronchial system (hyperreactivity) that reacts to non-specific triggers such as pollutants, cold air, or cigarette smoke. The typical course of allergic bronchial asthma begins with symptoms of a simple bronchitis, such as a dry, irritating cough and thick mucus production. The sticky mucus produced by the swollen mucous membranes narrows the bronchi, impairs breathing (shortness of breath), and causes the typical wheezing sound associated with bronchial asthma. In addition to mucosal swelling, many affected individuals also report difficulty in clearing the mucus.

Main symptoms of allergic bronchial asthma:

• Abnormal breathing sound (wheezing)
• Breathing difficulties
• Coughing

An allergy to house-dust mites is an important risk factor for the development of bronchial asthma. It is responsible for clinical symptoms in about 18% of asthma patients in Europe.

Neurodermatitis, also known as atopic dermatitis, is a chronic skin condition that occurs in flare-ups. Affected individuals suffer from dry, cracked skin that often itches and can become inflamed. Particularly infants and children are affected – in most cases, the condition disappears by puberty. The cause of neurodermatitis cannot be attributed to a single factor; rather, it is the result of a combination of different triggers.

Causes and Symptoms of Neurodermatitis

In clinical practice, family history is often considered because neurodermatitis has a strong genetic component. The cause is believed primarily to be an inherited disorder of the immune system. Contact with normally harmless substances such as house dust or certain foods triggers an excessive production of IgE antibodies in affected patients. The body responds with inflammation.

A Risk Factor for Neurodermatitis

The development of neurodermatitis is often caused by a disruption of the skin barrier, which can be genetically determined. For example, carriers of variants of the filaggrin gene cannot produce functional filaggrin protein, which leads to a severe impairment of the skin’s barrier function. The structural protein filaggrin plays a central role in the proper keratinisation of the epidermis as well as in maintaining the skin’s composition with sufficient levels of ceramides (lipids) and natural moisturising factors, which protect against skin dryness. The consequence of a genetically caused filaggrin deficiency is cracked, dry, and sometimes inflamed skin areas. Allergens and microbes can more easily penetrate the skin barrier and enter the skin. To protect the skin, continuous skincare is recommended to ensure adequate supply of fats and moisture. During flare-ups, treatment with corticosteroid-containing ointments can provide relief.

Factors that May Induce a Neurodermatitis Flare-up

• Activities that cause dehydration of the skin (frequent showering, bathing, hand washing)
• Contact with allergens through food, pollen, house-dust, etc.
• Substances that cause skin irritation (clothing, cosmetics)
• Stress
• Infections
• Excessive sweating
• Etc.

The diagnosis of an allergy is a complex process. A wide range of tests and diagnostic methods are available. They should be used depending on the symptoms and suspected allergy. Not every diagnostic procedure is suitable for detecting all types of allergies or intolerances. Therefore, it is particularly important to identify possible triggers in advance and select the appropriate diagnostic method. For this purpose, in vivo tests (such as prick skin tests and patch tests) are available, as well as laboratory blood tests (in vitro).