The skin of the back on that patch testing are made must be intact, i.e. devoid of any skin: acne, Folliculitis, psoriasis, Eczema of any nature, of irritation Dermatitis, pityriasis versicolor, pityriasis rosé rosea.
Eczema, in particular, is to reject (status eczematicus) because it would cause false reactions. In the event of excessive Hairiness, a prior shaving will be performed, ideally 24 to 48 hours before the application of the tests (to avoid any residual irritation due to shaving).
Make sure not to proceed with the application of the tests on benign skin tumors, such as prominent moles or seborrhoeic warts for example. A dorsal naevus dermatoscopique may be performed as a screening. The skin shall be no prior preparation for the application of the tests. It should be noted that ether degreasing is no longer topical.