The itch causes sneezing. Antihistamines work by blocking the effect of histamine. The stuffiness, which takes a little longer to respond, can also resolve. This is because the leaked fluid can be reabsorbed by the body and the antihistamine prevents further swelling. These medicines are often used, either alone or in combination with a decongestant, for the treatment of cold symptoms.
Some people find that antihistamines reduce the runny nose of a cold and help the tickle.
Since colds aren't caused by allergy, however, the beneficial effect of antihistamines for the cold is less than for allergy. Like all medications, antihistamines have a few side effects. The most common one is that of sedation. Different preparations have different amounts of this side effect and some people react more to some than others. This side effect can have its uses.