Signs and Symptoms
The two types of hypersensitivities commonly associated with the term "allergies" are type I immediate hypersensitivities and type IV delayed hypersensitivities.
- On the skin, an acute type I allergic reaction causes hives, dermatitis, and itching, while chronically, the allergy may cause atopic dermatitis and eczema.
- In the respiratory tract, an acute allergic reaction causes coughing, nasal congestion, sneezing, throat tightness, and, chronically, asthma. It can also cause red, itchy eyes.
- Acute allergic reactions in the gastrointestinal system start in the mouth with tingling, itching, a metallic taste, and swelling of the tongue and throat, followed by abdominal pain, muscle spasms, vomiting and diarrhea, chronically leading to a variety of gastrointestinal problems.
Type I allergic reactions can be variable in severity, with symptoms ranging from mild and short-lived to serious and life-threatening. Any severe, acute allergic reaction has the potential to be life-threatening, causing anaphylaxis, a multi-organ reaction that can start with:
- A feeling of "impending doom"
- Pale skin due to low blood pressure
- Loss of consciousness (fainting)
Examples of other signs and symptoms of anaphylaxis include:
- Red rash, hives
- Swollen throat, trouble swallowing
- Wheezing, trouble breathing, tightness in the chest
- Vomiting, diarrhea, cramping
Anaphylaxis can be fatal without the rapid administration of an epinephrine (adrenaline) injection.
Type IV signs and symptoms:
Type IV delayed hypersensitivity reactions are most often skin reactions. A common example is the reaction to nickel in metal jewelry. Type IV hypersensitivity may cause redness, swelling, hardening of the skin, rash, and inflammation of the skin (dermatitis) at the exposure site hours to days after exposure.