Urticaria is the medical term for hives, a common allergic reaction that affects about 20% of people at some point in their lives. There are many triggers for hives, but the symptoms include itchy patches of skin that become swollen red welts. Itching can be mild to severe, and may be made worse by scratching, alcoholic beverages, exercise, and stress.
Many people are aware of their triggers for hives, such as eating foods including shrimp or peanuts which cause the allergic reaction within a short time. For others, there are so many possible causes of hives it requires allergy testing by a physician. In a small number of cases the cause may never be identified.
Sinusitis is an infection or inflammation of the sinuses. A sinus is a hollow space. There are many sinuses in the body, including four pairs inside the skull. They serve to lighten the skull and give resonance to the voice. These sinuses are lined with the same kind of tissue that lines the inside of the nose. The same things that can cause swelling in the nose—such as allergies or infection—can also affect the sinuses. When the tissue inside the sinuses becomes inflamed, mucus discharge is increased. Over time, air trapped inside the swollen sinuses can create painful pressure inside the head. This is a sinus headache.
Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine chlorination and purification of drinking water supplies.  Recent research has shown that some common parasites , such as intestinal worms (., hookworms ), secrete chemicals into the gut wall (and, hence, the bloodstream) that suppress the immune system and prevent the body from attacking the parasite.  This gives rise to a new slant on the hygiene hypothesis theory—that co-evolution of humans and parasites has led to an immune system that functions correctly only in the presence of the parasites. Without them, the immune system becomes unbalanced and oversensitive.  In particular, research suggests that allergies may coincide with the delayed establishment of gut flora in infants .  However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms.  Clinical trials have been initiated to test the effectiveness of certain worms in treating some allergies.  It may be that the term 'parasite' could turn out to be inappropriate, and in fact a hitherto unsuspected symbiosis is at work.  For more information on this topic, see Helminthic therapy .