What may be behind skin irritation

What is contact allergy?

A contact allergy is an immunological reaction in which the immune system becomes oversensitive to certain substances that come into contact with the skin. It is a so‑called delayed‑type allergy (type IV), where symptoms do not appear immediately after contact but typically after 24 hours up to three days.

The allergic defence develops over time when the skin is repeatedly exposed to the triggering agent. The immune system then "learns" to react. Once sensitisation has occurred, even small amounts of the substance are sufficient to trigger the allergic reaction.

A characteristic of contact allergy is that usually only the areas of skin that were directly in contact with the allergenic substance are affected. However, the symptoms can be severe enough to significantly impact daily life or work.

Common allergens in contact allergy: what causes it?

Contact allergy is caused by substances that provoke an immune reaction when in contact with the skin. Common examples include metals such as nickel, found in jewellery, buttons, glasses or cookware, as well as cobalt and chromium, which can be present in cement or tanned leather. Fragrances in perfumes, cosmetics and skin care products, and preservatives such as formaldehyde and isothiazolinones are also important triggers.

Plant‑based remedies such as arnica, tea tree oil or bee resin (propolis) can also be potential allergens. Other common substances include colophonium, a resin used in plasters, and paraphenylenediamine, which is found in hair dyes. Latex, tattoo inks and chemicals in detergents or fabric softeners can also cause contact allergy.

Some allergies arise from cross‑reactions, where substances with similar chemical structures provoke a skin reaction. In rare cases, consumption of nickel‑containing foods such as chocolate or legumes may trigger an allergic eczema in people allergic to nickel.

Occupational exposure to allergens such as cement, chemicals or plants can significantly increase the risk of developing an allergy, especially when exposure continues for months or years. Other risk factors for contact allergy development include genetic predisposition, smoking, a high‑fat diet, excessive hygiene and exposure to environmental pollutants.

What are the symptoms of a contact allergy?

Symptoms of a contact allergy usually appear one to three days after exposure to the triggering substance and show up as various skin changes. Typical signs include redness, swelling, blisters that may ooze and hives. In some cases crusts or scaling develop. Affected areas may also itch or burn. With prolonged skin contact, a chronic form of contact allergy can develop, where the skin thickens and hardens (lichenification).

Symptoms generally remain, at first, limited to the skin areas that were directly in contact with the allergen, such as the hands, face — especially eyelids and lips — neck, as well as lower legs and feet. In fair‑skinned people the hypersensitivity reaction often appears as a reddish, poorly demarcated rash. In people with darker skin tones it commonly appears as a dark‑violet to dark‑grey discolouration, often accompanied by nodule formation and skin thickening.

In stronger reactions pain and a tight, tense feeling can occur. When blisters burst, the skin can ooze and later crust and scale. In some cases hypersensitivity reactions also occur on body areas that were not in direct contact with the allergen. These so‑called disseminated reactions are a characteristic feature of contact allergy.

Contact allergy: how is the diagnosis made?

Diagnosis of a contact allergy is carried out in several steps, starting with a detailed medical history. The doctor will ask targeted questions about known allergies, potential triggers in everyday life, occupational activities and the use of cosmetics or skin care products.

It is also important to distinguish an allergic reaction from a toxic reaction, for example to cleaning agents, which can also cause skin irritation. The aim is to narrow down the suspected cause of the skin symptoms, particularly when they are due to prolonged contact with a certain substance.

To confirm the diagnosis an epicutaneous test (patch test) is often performed, where patches containing suspected allergens are applied to the patient's back. After 24 to 72 hours it is checked whether a skin irritation, such as a small rash or eczema, appears. This test is read in several phases to ensure delayed sensitivity reactions are detected. If necessary, specific allergens relevant to the workplace or the individual case, such as leather components, chemicals or disinfectants, are tested.

In some cases a photopatch test can be useful to check for photoallergic reactions. Certain substances are exposed to UV light to determine whether the skin irritation is triggered by the combination of light and the tested substance.

The exact selection of substances to be tested is made individually, based on the history and the doctor's suspicion. Even if the test shows a positive reaction, this does not always mean a clinically relevant allergy is present, as it may reflect only sensitivity to the substance.

Can a contact allergy be completely cured?

A contact allergy is unfortunately not completely curable, since sensitisation to the allergen generally persists for life. This means the affected person will continue to react to the substance they have been in contact with previously. If the allergenic substance contacts the skin again, symptoms such as redness, itching or eczema will recur. The allergy itself cannot simply be "cured", as the body remains oversensitive to the substance.

The only way to control symptoms is to avoid contact with the triggering allergen. If this is implemented consistently, symptoms may resolve entirely in many cases, but this does not mean the allergy has disappeared. Especially in chronic cases it can be difficult to guarantee complete protection from the substance. Nevertheless, appropriate precautions can help minimise symptoms in the long term.

What you can do for a contact allergy: helpful tips

• Have your contact allergy accurately diagnosed by a dermatologist so the specific allergen can be identified and targeted treatment provided.
• For acute immune reactions use anti‑inflammatory medications such as corticosteroid ointments or creams with calcineurin inhibitors to soothe the skin quickly.
• Use only mild, soap‑free cleansers to spare the skin and avoid further irritation.
• When choosing perfumes, opt for products with few or no allergenic ingredients such as alcohol or synthetic fragrances.
• If you have a nickel allergy, replace stainless steel cookware with enamelled or heat‑resistant glass pans to avoid contact with nickel.
• Consider changing jobs or retraining if your allergy occurs at work and you are repeatedly exposed to the allergen.
• Avoid dyeing or colouring your hair, as even plant‑based hair dyes can trigger allergic reactions.
• Regularly use mild skin care products without fragrances and preservatives to protect your skin and minimise allergic reactions.
• Always wear protective gloves when working with cleaning agents or other potentially irritating substances to protect your skin.
• Apply an ointment or cream recommended by your doctor several times daily to strengthen the skin barrier and prevent irritation.

Contact allergies can be triggered by contact with certain substances and lead to unpleasant skin reactions. Early identification of the allergen and avoidance of triggers are key to reducing discomfort.