In medical terms, a cross reaction is a reaction between an antibody and the antigen that was created against a different antigen, which is altered but similar to original antigen. In physics, cross-reaction is an equal and opposite action given by a body against a force acting upon it.

A drug disulfiram has a severe cross-reaction with alcohol. Disulfiram has another name as tetraethyl-thiuram disulfide. Its trade name is Antabuse. This compound contains an unusual functional group of dithiocarbamate. Disulfiram has a high toxicity effect. Hence, it is used as a medication. It is administered in the patients who are seeking treatment for the alcoholism. The drug blocks the oxidation of alcohol at the acetaldehyde stage thus causes the patient to become very ill. The patient becomes ill even a very small quantity of alcohol is taken when the drug disulfiram is still present in the bloodstream. Some variety of mushrooms also have a cross reaction when taken along with alcohol.

Due to the cross reaction between food and inhalative allergens, 60% of adults suffer from food allergic reactions. Oral allergy syndrome or OAS is a type of food allergy caused by a bunch of allergic reactions in the mouth initiate due to eating several types of usually fresh fruits, vegetables or nuts. It typically develops in adult hay fever sufferers.

A cross reaction begins with one type of food and with reaction to others, which develops in later stages. Allergies to specific pollen are linked with OAS reactions to specific foods. The point to be kept in mind is that allergy to a type of food does not mean that the person will suffer from allergy for all the foods in that group. If a person is allergic to alder pollen then the person may suffer from OAS reaction to apples, hazel nuts, parsley, pears, celery, almonds, peaches, etc. An allergy with grass pollen may have an allergic reaction to melons, fig, oranges, tomatoes, etc. Some of the possible cross reaction to mugwort pollen, grass pollen, birch pollen, etc are citrus fruits like oranges, lemons, etc; berries like blueberries, raspberries, strawberries, etc; mango, figs, peanut, pomegranates, pineapple, grapes, etc.

People who are allergic to insects or mites like mosquito larvae, cockroaches and mosquitoes have a cross reaction to mussels, snails, oysters and crustaceans. Some individuals with latex allergy may develop allergic symptoms from interesting vegetables and fruits. Few examples for the symptoms of this cross-reaction are papaya, potatoes, figs, chestnut, tomatoes, kiwi fruit, avocado, etc. Effects of cross-reactivity on clinical performance were estimated by calculating sensitivity and specificity..