An allergic reaction is the body's way of responding to an "invader." When the body senses a foreign substance, called an antigen, the immune system is triggered. The immune system normally protects the body from harmful agents such as bacteria and toxins. Its overreaction to a harmless substance (an allergen) is called a hypersensitivity, or allergic, reaction.
- Anything can be an allergen. Common dust, pollen, plants, medications, certain foods, insect venoms, viruses, or bacteria are examples of allergens.
- Reactions may be in one spot, such as a small skin rash or itchy eyes, or all over, as in a whole body rash.
- A reaction may include one or several symptoms.
In rare cases, an allergic reaction can be life threatening, although most allergic reactions are much less serious, such as a rash from poison ivy or sneezing from hay fever. The reaction depends on the person but is sometimes unpredictable.
Allergic reactions are unique to the individual. Most people are aware of their particular allergy triggers and reactions.
- Certain foods, vaccines and medications, latex rubber, aspirin, shellfish, dust, pollen, mold, animal dander, and poison ivy are famous allergens.
- Bee stings, fire ant stings, penicillin, and peanuts are known for causing dramatic reactions that can be serious and involve the whole body.
- Minor injuries, hot or cold temperatures, exercise, or even emotions may be triggers.
- Often, the specific allergen cannot be identified unless you have had a similar reaction in the past.
Allergic Reaction Symptoms
The look and feel of an allergic reaction depends on the body part involved and the severity of the reaction. Some reactions affect many areas, others affect just one area. Reactions to the same allergen vary by individual.
Anaphylaxis is the term for any combination of allergic symptoms that is rapid, or sudden, and potentially life threatening. Allergic reactions can be dangerous. Sudden, severe, widespread reactions require emergency evaluation by a medical professional.
- Sudden, severe, rapidly worsening symptoms
- Exposure to an allergen that previously caused severe or bad reactions
- Swelling of the lips, tongue, or throat
- Wheezing, chest tightness, loud breathing, or trouble breathing
- Confusion, sweating, nausea, or vomiting
- Widespread rash
- Collapse or unconsciousness
- One sign of anaphylaxis is shock. Shock is caused by sudden dilation of many or large blood vessels. This is brought on by the action of the mediators. If the drop in blood pressure is sudden and drastic, it can lead to unconsciousness, even cardiac arrest and death.
- Symptoms of an allergic reaction include any, some, or many of these:
- Skin - Redness, itching, swelling, blistering, weeping, crusting, rash, eruptions, or hives (itchy bumps or welts)
- Lungs - Wheezing, tightness, cough, or shortness of breath
- Head - Swelling of the face, eyelids, lips, tongue, or throat; headache
- Nose - Stuffy nose, runny nose (clear, thin discharge), sneezing
- Eyes - Red (bloodshot), itchy, swollen, or watery
- Stomach - Pain, nausea, vomiting, diarrhea, or bloody diarrhea
Image courtesy U.S. Food & Drug Administration
Common sites for allergic reactions