Alkaline neutralization test

Orienting test to assess the alkaline neutralization capacity of the skin, especially in toxic-degenerative eczema.

1/80 normal NaOH solution is applied drop by drop to a marked area of skin (usually the back of the hand or forearm flexion side), then a drop of 0.5% alcoholic phenolphthalein solution is added so that a reddish coloration appears; now a small glass block is placed on the skin and carefully moved. The time between the placing of the glass block and the decolouration of the solutions is recorded by the stopwatch. Out of 10 measurements, the shortest and the longest are discarded. Neutralisation times of more than 7 minutes are considered pathological, see also Nitrazine yellow test.