Research involved comprehensively reviewing all published information on allergies and cancers. We located 119 papers (1955-2005), which reported results of 278 studies of individual types of allergies and 129 studies of multiple allergies combined in relation to cancers of 19 specific tissues and organ systems or multiple cancers combined. Overall, 0.44 of studies of specific allergies and 0.44 studies of multiple allergies combined reported that people diagnosed with a cancer were less likely to have expressed allergy symptoms (coughing, itching, tearing, diarrhea) prior to their diagnosis than matched comparison groups of non-cancer patients. By contrast, only 0.18 of studies of specific allergies and 0.16 of studies of multiple allergies combined reported that cancer patients were more likely to have expressed allergy symptoms prior to diagnosis than non-cancer comparison groups. The remaining studies of specific allergies (0.37) and of multiple allergies combined (0.40) found no relationships with cancers. There was a significant excess of inverse allergy-cancer relationships over positive and null relationships. Allergy-cancer relationships also differed among types/sites of cancers: inverse relationships were significantly more frequent for cancers of eight tissues and organ systems that directly interface with the external environment than for cancers of eight tissues and organ systems that do not interface with the external environment.

Allergies affect people worldwide. In the U.S. alone more than 90 million people suffer from allergies (one in three Americans), and treatment costs exceed $19 billion annually. Most of this money is spent on suppressing allergy symptoms. But why do we have allergies in the first place? Conventional wisdom says that they are merely disorders of the immune system. But might they actually provide some benefit? If so, then can allergy symptoms be suppressed with impunity, as is commonly done, or would people be better off if they worked with instead of against their allergies? Is there, in fact, some long-term health cost to eliminating allergy symptoms?

Research involved comprehensively reviewing all published information on allergies and cancers. We located 119 papers (1955-2005), which reported results of 278 studies of individual types of allergies and 129 studies of multiple allergies combined in relation to cancers of 19 specific tissues and organ systems or multiple cancers combined. This is the most complete and comprehensive data base of its kind in existence. The data were used to test three alternative hypotheses: (1) antigenic stimulation (allergy symptoms increase cancer risk because chronic inflammation and stimulation of cell growth provides frequent opportunities for mutations and malignant proliferation of actively-dividing stem cells), (2) prophylaxis (allergy symptoms reduce cancer risk by binding heterospecific cells, toxins, and foreign particles with mucous and expelling them before they, and any contained or adhering mutagens, can trigger carcinogenesis), and (3) immunosurveillance (allergy symptoms do not directly affect cancer risk, but allergies and cancers are inversely related because immune systems that are especially capable of detecting and attacking pre-malignant autogenic cells also are adept at recognizing and eliminating heterospecific cells, toxins, and foreign particles).

Results were most consistent with the prophylaxis hypothesis: normal (sub-lethal) allergy symptoms help protect certain tissues from cancer, especially tissues that are routinely exposed to environmental toxins, microorganisms, and particulate matter such as dust, pollen, smoke, and mold to which mutagenic chemicals may be adhering. In addition, allergy symptoms may function as personal "smoke detectors," indicating what environmental chemicals and particles any particular individual should avoid contact with (i.e., breathing, eating, or drinking). In turn, this raises the $18 billion question: should allergies be routinely suppressed (via densensitization or antihistamines), or would world health be improved (and cancer rates be reduced) by working with and heeding the implied message of allergy symptoms? Our study raises these questions for the first time, and points the way toward the need for research that assesses the benefits of allergies to people of different ages, sexes, familial histories of cancers, and environmental exposures versus the costs of allergies (financial, physical, and emotional).

Ms. Erica Holland (Private Consulting Firm)