Basale

The highest concentrations of 7-dehydrocholesterol are found in the epidermal layer of skin—specifically in the stratum basale and stratum spinosum.

The two most important factors that govern the generation of pre-vitamin D 3 are the quantity (intensity) and quality (appropriate wavelength) of the UVB irradiation reaching the 7-dehydrocholesterol deep in the stratum basale and stratum spinosum.