Lack of interference in skin tests by histamine in food extracts.

Because histamine occurs naturally in some food products, quantitative analysis of the histamine content of extracts of food used for skin testing seemed desirable to determine its effect in the production of positive reactions. Up to 200 nanograms of histamine per milliliter were found in some food extracts. When the extracts are diluted to 1:100 and 1:1000 W/V for skin testing the amount of histamine which would be injected in a intradermal skin test is one-thousandth of the amount required to produce a significant wheal. Therefore the histamine content of the foods analyzed is too small to be of practical concern and not enough to give nonspecific wheal reactions in intradermal tests using extracts of 1/1000 or 1/100 W/V concentrations. Nonspecific reactions in skin tests are probably most often due to use of food extracts of unnecessarily high concentration.