Does mineral oil stop other ingredients from reaching your skin?

Kitster’s question…I’m a bit confused about mineral oil. Is it absorbed into the skin at all or does it just sit on top of the skin forming a layer? My favourite moisturiser is mineral oil based and I use physical sunscreen on top of it which contains some good stuff for skin eg antioxidants etc. So does the mineral oil in my moisturiser prevent ingredients in my sunscreen from reaching my skin?

The Beauty Brains respond:

First of all, let’s clarify that mineral oil (M.O.) only penetrates into the upper layers of the stratum corneum. It is not absorbed through the skin into the dermis. It does form a film although that film is not necessarily entirely contiguous – in other words there will be gaps in the film. In moisturizing lotions, this film does a good job of keeping water from getting OUT of the skin because it is so hydrophobic. But, to paraphrase your question, does the film keep other ingredients from getting TO the skin?

Mineral oil is used in sunscreens

Based solely on the fact that mineral oil is used in sunscreens, I have to say the answer is no. That’s because when M.O. containing sunscreens are tested they are shown to provide UV protection which indicates that the sunscreen active is getting to the upper layers of of skin. This diffusion takes a little while which is why you should put sunscreen on 30 minutes before going into the sun.

Mineral oil does not stop drug penetration

If that’s not proof enough, I found a study which evaluated the effect of varying the water and mineral oil ratio on the diffusion rate of sulphathiazole from cold cream type ointments. In this study they took creams that contained from 8% to 83% mineral oil and measured how well a specific drug ingredient diffused out of the cream. The study was done in the lab, not on skin, but the results showed that even at the highest level of M.O the drug still diffused through the cream. Granted though, it diffused much faster at lower levels. Mineral oil is rarely used at very high levels in creams so this indicates there’s not really any problem.

The Beauty Brains bottom line

Considering that sunscreens are demonstrated to be efficacious even when they contain mineral oil (and considering that at least some active ingredients have been shown to diffuse through mineral oil) it doesn’t seem like there’s much to be worried about.