Email Question: How permeable is your skin to chemicals?

New segment time! Also widely known as Chris has had a busy week but still wants to keep up appearances on his blog so that people don't think he's quitting or anything. Once in a while, I get drug and/or poison-related questions emailed to me. I usually try and respond to the best of my abilities, which for the most part consists of referring to my textbooks and pulling stuff out of my butt. Here is a question email I received a while back:

My mom and I have been having kind of a dispute about the permeability of chemicals to your skin. She believes that your skin breathes and that's why you can't cover it, as brought fourth [sic] in the James Bond movie. She takes it one step further to say that things like lotions
can be absorbed by your skin and have adverse health affects similar to eating the lotion. I disagree, the skin outright has no structure or role in breathing. I understand that some things can be absorbed by the skin, like the chemicals in nicotine and pregnancy patches, I've also read that in the 70's that there was a scare of people putting LSD on doorknobs because it can be absorbed through the skin.

So my question is, what really defines permeability to the skin, and what are or is a common carrier for dermal-permeable chemicals?

- Dave


Hey Dave,

Okay, so first off, the skin has no role in breathing. I'm assuming we're defining breathing as gas exchange between air and blood, which is an exclusive function of the lungs.

Covering your skin in an impermeable substance like gold would cause you to lose the ability to sweat AND you would no longer be able to effectively lose heat through your skin. Consequently, you would be unable to effectively regulate your body temperature, and so would overheat and potentially die as a result.

One of the primary purposes of the skin is to provide a barrier to block the entry of virtually all substances into your body. However, said barrier is not entirely effective, such that most chemicals will be able to pass through the skin, albeit usually at levels insufficient to cause any effect, into the bloodstream. This process is comparable to eating the chemical and it being absorbed in your intestine into your bloodstream.

The permeability of the skin to a chemical is dependent on the lipid solubility of the chemical, that is, how readily it will dissolve into fat relative to into water. Chemicals that prefer to dissolve into fat will be absorbed to a greater extent via the skin. Chemicals that are not very lipid soluble can be suspended in an oily vehicle to enhance their ability to enter the body through the skin. Even so, giving a drug via the skin (percutaneously) is generally not considered an efficient method for getting the drug into the bloodstream, except in the case of patches for nicotine, sex hormones, scopolamine (for motion sickness), and nitroglycerin (for angina). All of these drugs are highly lipid soluble.

LSD is incredibly potent, so it only takes a really tiny amount for you to start tripping out. Thus, even though it is poorly absorbed through the skin, it can still cause effects that way.

Hope this all made some sense. Thanks for reading the blog!

Chris