A University of Pittsburgh Graduate School of Public Health study into the skin absorption rates of contaminants in public drinking water found that the skin absorbed an average of 64% of the total contaminant dosage. Another study found the face to be 2-6x more permeable than broad body surfaces, and underarms and genitalia to be even more permeable.
They recommended a 100% absorption estimate for the later areas (Kasting, 2005). Studies also show the absorption varies depending on the compound. For instance, caffeine is absorbed through the skin at 48% while DDT is absorbed at 10%. For fragrance ingredients, a commonly used approach is to assume 100% absorption (Robinson et al, 2000).
Regardless of the actual percentages, it is quite clear that a lot of what we apply on our skin ends up in our bodies. So it makes good sense for us to pay attention to the ingredients that are in our skin care products. Choosing natural and organic ingredients immediately cuts out a lot of preservatives, fragrances and color compounds that are suspect to be harmful to us. While not all naturally derived ingredients are good for us, you can be assured that with a certified natural or organic product, extra effort has been taken in the interest of health and cost-saving short cuts avoided.