(HealthDay News) -- Angioedema is the medical term for hive-like swelling beneath the skin. It's often caused by an allergic reaction.

The U.S. National Library of Medicine mentions these common triggers for angioedema:

• Outdoor allergens, such as pollen.
• Animal dander.
• Exposure to significant heat, cold, sunlight or water.
• Foods that cause allergies in many people, such as milk, nuts, shellfish or eggs.
• An insect bite or sting.
• Certain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), blood pressure drugs, and certain antibiotics such as penicillin.

If someone has difficulty breathing in addition to the swelling, seek emergency medical treatment immediately.