Studies on nano-sized titanium dioxide and zinc oxide have shown they do not absorb past the uppermost layers of skin (9). Other types of UV filters, such as oxybenzone, octinoxate, octocrylene, and octisalate can be absorbed by the body, but the amount is so minimal it's barely measurable. The amounts are typically measured in nanograms, or one-billionth of a gram (picture adding one drop of water to a swimming pool).