Colour change in the human histamine wheal made visible by LYYN: a technique to enhance colour differences.

Background: Colour differences in photographs can be enhanced using a digital image-processing technique called LYYN. Objective: To investigate colour changes in the histamine wheal after skin prick tests (SPTs). Methods: Histamine SPTs were performed on the forearm of six medical students, and the reactions of the skin were photographed every 2 min for 30 min. Colour differences in the photographs were then enhanced using the LYYN technique. These images were processed using ImageJ to yield numerical values. Results: In the LYYN-processed images, there was a rapid colour change in the histamine wheals between the 18th and the 20th minute (P<0.01). Histamine perfusion in isolated rabbit ears indicated vasodilatation in post-capillary vessels and desensitized histamine 1 (H1) receptors after a mean of 17 min. It is possible that a similar desensitization takes place in the human histamine wheal, and a study of two histamine SPTs 90 min apart at the same site supports this hypothesis. Conclusion: The LYYN technique was sensitive enough to discover a rapid colour change in the histamine wheal, a change that has not been described before.