Role in enhancing skin barrier function
While perhaps not as commonly used as vapes or edibles, topical products are a unique way to administer medical cannabis. Topicals possess many advantages as an alternative method, as patients who are not comfortable with broadcasting their cannabis use to the world can use lotions or creams discreetly. Topicals are also beneficial for targeting certain areas like the hands, back, or legs.
Topicals can also take effect rapidly, as they bypass the stomach and digestive system, going straight through the skin to the bloodstream.  But the benefits of topicals don’t stop there. In fact, for some dermatological conditions, topical cannabis might actually exert its effects by enhancing function of the skin barrier.
Atopic dermatitis (AD) is a condition characterized by chronic inflammation and uncomfortable itching. Research on the mechanism of AD has revealed damage to skin barrier function due to the effects of pro-inflammatory substances like cytokines. 
Several cannabinoids are effective at relieving AD symptoms, likely due to their anti-inflammatory properties. [3, 4] Several studies have dug further to better understand the mechanism underlying these effects.
Treatment with oxazolone solution (1% in acetone) mimics the effects of AD in pre-clinical models. Using this technique, as well as cell assays, researchers found that CB1 receptor agonists (which increase the function of the receptor) inhibit the production of inflammatory compounds linked to AD. 
An additional study employing the same AD model confirmed these findings. However, researchers also found that CB1 agonists significantly accelerated and improved skin barrier recovery based on measuring epidermal permeability barrier markers. 
These results support the use of cannabinoids like palmitoyl ethanolamide, or PEA. In fact, this endocannabinoid has been used to treat dermatological conditions like AD.  While PEA is a CB2 agonist, it stimulates anandamide, another endocannabinoid, to activate the CB1 receptor. These actions in turn alleviate itch. [3, 4, 6]
While there are many benefits of topical cannabis use, a greater understanding of how cannabinoids exert their effects on dermatological conditions like AD may help when choosing the right therapy. For example, knowing which cannabis compounds work directly via the CB1 receptor or CB2 receptor (or outside of the cannabinoid system altogether) can help you in discussing a plan with your doctor or dispensary.
However, it’s also important to keep in mind the benefits of the “entourage effect,” or the power of full-spectrum cannabis brought on by both cannabinoids and terpenes.  So, if you haven’t used cannabis topicals before, trying out different products may be best to determine what works best for you and your condition.
- Huestis, M.A., “Human Cannabinoid Pharmacokinetics.” Chem Biodivers. vol.4, no.8, 2007, pp.1770-1804.
- Kim, H.J., et al., “Topical Cannabinoid Receptor 1 Agonist Attenuates the Cutaneous Inflammatory Responses in Oxazolone-induced Atopic Dermatitis Model.” Int J Dermatol. vol.54, no.10, 2015, pp. e401-408.
- Mounessa, J.S., et al., “The Role of Cannabinoids in Dermatology.” J Am Acad Dermatol. vol.77, no.1, 2017, pp. 188-190.
- Eagelston, L.R.M., “Cannabinoids in Dermatology: A Scoping Review.” Dermatol Online J. vol.24, no.6, 2018, pp. 1-17.
- Nam, G., et al., “Selective Cannabinoid Receptor-1 Agonists Regulate Mast Cell Activation in an Oxazolone-Induced Atopic Dermatitis Model.” Ann Dermatol. vol.28, no.1, 2016, pp. 22-29.
- Borrelli, F., “Palmitoylethanolamide, A Naturally Occurring Lipid, Is An Orally Effective Intestinal Anti-inflammatory Agent.” Br J Pharmacol. vol.172, no.1, 2015, pp. 142-158.
- Russo, E.B., “Taming THC: Potential Cannabis Synergy and Phytocannabinoid-terpenoid Entourage Effects.” Br J Pharmacol, vol.163, no.7, 2011, pp.1344-1364.