Humans have been rubbing oily extracts of the cannabis plant into our skin for a very long time. The plant is mentioned several times (as “kaneh-bosem,”) in the Old Testament (as per Yahweh’s instruction to Moses in Exodus 30:23) as an ingredient in holy anointing oil. At that time in history, the word messiah simply meant “the anointed one.” Even if this reference is not historically accurate, marijuana was an important medicinal plant to our ancestors.
Today, over-the-counter gels containing CBD are for sale everywhere. Do these products offer any health advantages for your skin? The answer, thus far, is yes. Recent studies using rats suggest that transdermal CBD has beneficial anti-inflammatory effects on the skin. If this is also true for humans, then CBD ointments should provide relief to people who suffer from dermatitis (eczema), rosacea, seborrheic dermatitis, and psoriasis. The application of CBD to the skin of mice increased the proliferation and wound-repair chemicals in keratinocytes, which are the epidermal cell that produces keratin. The authors concluded that their results support the use of topical CBD for the treatment of atopic dermatitis and keratin disorders as well as for enhancing wound healing.
With regard to whether topical CBD can influence the brain, a number of factors become important. The challenge in applying any drug to the skin is that the drug must first penetrate the dead superficial layer of skin in order to become absorbed into the blood. The amount of CBD that gets into the blood is greater if the skin is abraded, burned, or inflamed; obviously, these are not ideal conditions for regular use.
So, can CBD get across the skin and into the blood? Yes. A much more important question is whether it can reach an adequate level in the blood in order to affect your brain function. Once the CBD is absorbed into the blood it will distribute first to the body fat. Thus, for the majority of big adults who carry extra body fat, the amount of CBD that gets into the blood will be quickly absorbed into the fat and not the brain. Therefore, you may need to apply a lot of gel.
A recent study examined the ability of THC to get across the skin and reported that levels of THC were undetectable after being applied via a topical cream. However, CBD is ten times more permeable in the skin than THC. If CBD is embedded in a transdermal patch, or in a transdermal gel, which is designed to enhance absorption, then it can gain access to the blood. A recent study applied the gel twice a day to the skin for 12 weeks (that’s a long exposure) and reported a significant decrease in the level of anxiety in children with Fragile X syndrome. It’s important to note that children are smaller and have less body fat and would require that less CBD reach the blood in order to affect the brain.
There is still very little human data on this topic that is reliable. When CBD was applied as a transdermal gel to the skin of guinea pigs, the level of CBD peaked at 6.3 ng/mL of plasma after about 12 hours. When CBD was applied in a transdermal gel to the skin of rats, the level of CBD reached almost 400 ng/ml of plasma and the authors reported a reduction in anxiety and impulsivity. You can easily see that the challenge is getting enough into the blood.
The application of CBD dissolved in transdermal gels offers some unique advantages. Oral absorption of CBD is not as efficient as inhalation and is associated with gastrointestinal side effects. For some people, inhalation is not an option. These preliminary studies encourage further studies of the usefulness of topical application as compared to oral or inhalation methods in humans.
© Gary L. Wenk, Ph.D. is the author of Your Brain on Food, (3rd Edition, 2019; Oxford University Press) and is a member of the Governor’s Medical Marijuana Advisory Committee for the State of Ohio.
Casares L et al (2020) Cannabidiol induces antioxidant pathways in keratinocytes by targeting BACH1 REDOX BIOLOGY, vol 28, Article No: UNSP 101321
Gonzalez-Cuevas G et al (2018) Unique treatment potential of cannabidiol for the prevention of relapse to drug use: preclinical proof of principle. NEUROPSYCHOPHARMACOLOGY Vol 43, p 2036