The immune system has evolved to protect the body from external invasions of pathogenic microorganisms or from internal problems (like cancer or viral infections). Thus an immune system is sensitive to an immunogen (a foreign substance capable of eliciting an immune response) and it responds aptly to its presence. Under certain circumstances, it can give an inappropriate response against an innocuous immunogen. This leads to an allergic response.
Allergies occur due to a wide variety of allergens (allergy-causing agent). These could be food allergies, respiratory allergies or skin allergies. Food allergies could manifest as nausea, vomiting, difficulty in swallowing and breathing and diarrhea. Respiratory allergies could manifest as either hay fever (allergic rhinitis), when the upper respiratory system is involved and asthma, when the lower respiratory system is involved. Skin allergies usually occur due to a contact antigen.
Eczema (Atopic Dermatitis)
Eczema is a chronic disease that is more common in childhood than in later stages of life. It is a recurrent skin disease. It is an itch (pruritis) that when scratched develops into a rash (eczema). In young children, this condition, if present, is very severe, although it resolves as the child ages. This condition is atopic, i.e., the person has a tendency to develop an allergy. Hence, it is hereditary; someone in the family has a diagnosed allergy.
Eczema is usually seen on cheeks, chest and trunk in young children and in front of the elbow and behind the knee in older children or adults. Itching is generally triggered by a variety of factors like irritants, infections, allergens and stress. The most common allergens that can cause atopic dermatitis are those that can trigger itching when they come in contact with the skin, like animal dander and dust mites.
The best way to avoid this condition is to avoid irritants that can trigger itching. Skin should always be kept moisturized. Use of sunscreen lotion helps keep the skin protected from sunburns. Harsh soaps and detergents should be avoided and contact with animal dander should be prevented. In severe cases, medication is needed to control eczema. These include topical steroids, topical calcineurin receptors, oral steroids and oral and topical antibiotics to control skin infections.
Urticaria (Hives) and Angioedema (Swelling)
Urticaria is a disorder that affects as much as 20 percent of the population at some point in their lives. Angioedema, a swelling that usually accompanies urticaria, can lead to swelling of hands, face and feet. The rash in case of urticaria is raised (elevated), red and itchy. It can be small or large and smaller patches tend to coalesce, forming irregularly shaped areas. Angioedema does not itch but it stings and burns and can be severe in some cases. Urticaria and angioedema can be acute (lasting less than six weeks) or chronic (lasting more than six weeks). This condition can be controlled by antihistamines, which stop the activity of a chemical called histamine, whose activity is manifested as the symptoms. But this provides only symptomatic relief and is temporary.
Allergic contact dermatitis is caused by the contact of allergens like nickel, gold, balsam, thiomersal, neomycin, formaldehyde, cobalt and fragrance mixes. The most common contact allergens that can trigger this condition are chemicals called urushiols produced by members of the genus Toxicodendron (poison ivy, poison oak). This kind of dermatitis is also known as delayed type hypersensitivity since the symptoms appear 24 – 48 hours after actual allergen contact. A red rash, blisters and itchy, burning skin are common symptoms of allergic contact dermatitis. Topical application of corticosteroids and oral antihistamines are used to control this condition.