We discovered this technique in the book Dermatology: Diagnosis and Treatment* and have been using it ever since we wrote it up in the first edition of "The People's Pharmacy®."
Moderate itching (the sort of thing you get from a mosquito bite or mild case of poison ivy without blisters) often responds to a hot water application. The water needs to be hot enough to be slightly uncomfortable but not so hot that it burns (120-130 degrees Fahrenheit).
If you let the hot water tap run for a few minutes this should be about right. A few seconds' exposure is all you need to produce several hours of relief.
*Sulzberger, M. B., et al. Dermatology: Diagnosis and Treatment. Chicago: Yearbook, 1961; p. 94