Release of histamine will sometimes cause swelling of the eyelids, lips and tongue. Hives are usually not dangerous, but swelling of the lips can be alarming, and may indicate a more severe allergic reaction. If the tongue swells or any difficulty in breathing occurs immediate medical attention should be sought. Causes Many times it is very difficult to discover what allergen is inducing the hives. However, it can also be something applied to mucous membranes such as products used in the eyes, mouth, vagina, or rectum.
Injections are another common entry mechanism for allergens.
The least common trigger is something applied externally to the skin. Another possible source of the allergen is from within the body, very commonly an infection. Internal parasitic infestations also may induce hives. Sometimes hives are triggered by nervous tension and stress. Other less common inducers of hives are reactions to cold, heat, sunlight, water and physical exertion.