2 University of Colorado studies show that milk thistle extract (silibinin) kills UVA damaged skin cells and protects against UVB damage.
The extract has no effect on healthy skin cells but kills cells damaged by UVA radiation.
UVA rays don’t cause sunburn, but can damage the deep levels of our skin. They are responsible for the aging effects of sun exposure, like photoaging, wrinkles and sagging skin. Over exposure to UVA rays can also increase the risk of skin cancer – so those UVA tanning beds are not safe.
With the UVB radiation, the extract was found to provide protection. UVB rays are the ones to blame when you get sunburn and most skin cancers. They are most prevalent at mid day.
These studies were talking direct application to skin cells, so I don’t know what effect taking milk thistle as a supplement would have.
Can read the ScienceDaily study review here:
Silibinin, found in milk thistle, protects against UV-induced skin cancer
And about UVA and UVB rays here: