Skin Allergies: How to Recognise Them?

Skin allergies most commonly present themselves through redness, skin swelling and itching, although other symptoms may also appear. There are several types of skin allergies, the main ones being the contact eczema and urticaria.

• Contact dermatitis.

  Also known as allergic contact dermatitis, contact eczema is an inflammatory reaction that occurs after a direct contact between the skin and an allergenic substance. This type of reaction occurs in two phases: the sensitisation phase, when the allergen first comes into contact with the skin, and the elicitation phase, when the immune system recognises the substance after a second exposure. The lymphocytes then release lymphokines, a class of cytokines that direct the immune system's response and cause intense itching, redness, and small blisters.

  Inflammation also results in the dilation of blood vessels and an accumulation of fluid in the surrounding tissues, which causes swelling in the affected area. The mechanism of contact eczema is actually designed to isolate the allergen to prevent its spread throughout the rest of the body, but it is accompanied by bothersome symptoms. Generally, the first signs of contact eczema appear within 12 to 48 hours following exposure to the allergen.

• Urticaria.

  Unlike contact eczema, urticaria is a relatively rapid skin reaction. It manifests as raised, red or pink patches, accompanied by itching. Urticaria results from a sudden release of histamine and other mediators by mast cells, immune cells present in the dermis. Histamine causes an increase in vascular permeability, thus promoting the influx of fluid and immune cells to the affected tissues and causing a dilation of the blood vessels, which results in the characteristic red patches of urticaria.

  These can vary in size and shape and usually appear a few minutes to a few hours after exposure. The patches can migrate from one area of the body to another, evolving and disappearing without leaving a trace. The hives reaction is often triggered by foods, medications or nettle stings. Once again, the purpose of hives is to quickly isolate the allergen and mobilise the immune cells, although this causes significant discomfort for the person concerned.

• Quincke's Oedema.

  Quincke's oedema, or angioedema, is a very rare allergic reaction that can prove to be fatal. More profound, it affects the subcutaneous tissues. Quincke's oedema is triggered by a massive activation of mast cells and a significant release of inflammatory mediators such as histamine, which causes swelling of the underlying tissues. The mechanism of action of histamine is the same as in the case of urticaria: this inflammatory mediator increases vascular permeability and vasodilation and creates a swelling of the tissues. However, this swelling is significantly more extensive in the case of Quincke's oedema.

  This reaction often occurs on the face, eyelids, lips and sometimes the throat, where it can lead to a blockage of the respiratory tract. Even though Quincke's oedema is a rare skin allergic reaction, it is particularly dangerous as it can lead to swelling of the pharynx, potentially causing asphyxiation. Immediate medical attention is required at the first signs.

What to do in case of a skin allergy?

It's not always easy to identify the allergen responsible for an allergic skin reaction. If you're unable to determine the offending substance, it's best to consult a healthcare professional. Using a patch test, they can identify which allergen caused the skin allergic reaction, in order to avoid it in the future. Alongside this, to alleviate the symptoms of the allergy, doctors often prescribe antihistamines or corticosteroids.