An allergy is a physiologic reaction caused when the immune system mistakenly identifies a normally harmless substance as a substance that is damaging to the body. At University Health Care Dermatology Services, we perform thorough evaluations for both delayed and immediate type allergies.
Typically, the human immune system defends itself against harmful substances, such as viruses or bacteria, but sometimes it aggressively attacks normally harmless substances that the body is exposed to and considers them foreign. These immune/allergic reactions occur in two varieties: delayed and immediate reactions.
Skin Allergies: Delayed Vs. Immediate Reaction
Delayed reactions, or allergic contact dermatitis, is the most common allergic reactions that show on the skin and occur when various substances get on the skin, developing into an itchy rash a day or two later. A poison ivy rash is typical for a delayed allergy, but a similar type of reaction can occur after contact with shampoos, cosmetics, creams, earrings, and many other chemicals. Immediate immune reactions are those in which substances, such as mold, dust, pollen, or animal dander cause swelling of the nose or sinuses, asthma, or itchiness of the eyes within minutes of exposure. This is the reaction with typical seasonal allergies.
Symptoms of Delayed-Reaction Skin Allergies
- A rash that can be red, itchy, rough, scaly, crusty
- A blistering reaction
- Swelling of the skin
- Redness and swelling in the mouth
Symptoms of Immediate Reaction Skin Allergies
- Rhinitus (nasal stuffiness, sneezing, nasal itching, nasal discharge)
- Allergic conjunctivitis (red, itchy, watery eyes)
- A flare of atopic dermatitis (red, itchy, dry skin)
How Skin Allergies Are Diagnosed
Delayed allergies are evaluated through patch testing. This is a process in which various allergens are applied to the back with tape and left in place for two days at which time they are removed. The patient is brought back another two days later to evaluate for delayed reactions on the skin which present as red, swollen areas.
Immediate-type allergies are evaluated through either making a small scratch or prick in the skin through diluted allergens that are applied to the back. The evaluation/reading of this type of testing is done about 30 minutes later. Also, various blood tests can also be utilized to evaluate for this type of allergy as well.