“There are only two industries that call their customers ‘users’: illegal drugs and software”
— Edward Tufte, a computer scientist, said in The Social Dilemma Netflix 2020 Documentaries.
Less is More
Is 3% topical steroid far more potent than a 0.01%? Short answer, NO.
It is true that 0.25% betamethasone dipropionate is stronger than 0.05% betamethasone dipropionate, however the 0.05% clobetasol propionate is approximately 600-1000 times stronger than 1% hydrocortisone. It is important to remember that the strength of a steroid preparation is not proportional to the % displayed on the label. For example, a 0.01% class I steroid may be hundreds of times more potent compared to a 3% class VII preparation. Understanding how strong the product you received isn’t as easy as reading the label due to the many factors that are at play.
What is steroid potency?
Topical corticosteroids can be subdivided into seven classes in the United States based on their ability to constrict small blood vessels (also known as capillaries) [1,2], with Class One being the most potent and Class Seven the least potent. However, UK and France use four classes. The immunosuppressive effects of topical corticosteroids also acts directly on the DNA level [3-5], the higher the potency of a topical steroid, the higher the risk of getting side effects.
How is the potency determined?
The strength of a topical steroid is determined by a vasoconstrictor test that measures how much it can cause your blood vessels to constrict (blanching of the skin) after topcial applicaiton on healthy skin [6,7]. Investigators assess steroids penetration and their blanching effect with a chromameter to measure the exact skin colour, from absence to strong vasoconstriction. It is evident that the vasoconstriction rankings predicts not only percutaneous absorption but also the risk of side effects. Who can assume that the vasoconstriction on healthy skin is correlated with the anti-inflammatory effect on skin disease?
— 计算机科学家爱德华·塔夫特（Edward Tufte）在奈飞2020年纪录片《社会困境》中说。
- Humbert, P. and Guichard, A. (2015), The topical corticosteroid classification called into question: towards a new approach. Exp Dermatol, 24: 393-395.
- Cornell RC, Stoughton RB. Correlation of the vasoconstriction assay and clinical activity in psoriasis. Arch Dermatol 1985; 121:63.
- Ahluwalia A. Topical glucocorticoids and the skin–mechanisms of action: an update. Mediators Inflamm. 1998;7(3):183-93
- Uva L, Miguel D, Pinheiro C, Antunes J, Cruz D, Ferreira J, Filipe P. Mechanisms of action of topical corticosteroids in psoriasis. Int J Endocrinol. 2012;2012:561018
- Sarah Gabros; Trevor A. Nessel; Patrick M. Zito. Topical Corticosteroids. Treasure Island (FL): StatPearls Publishing; 2022 Jan
- Goa KL. Clinical pharmacology and pharmacokinetic properties of topically applied corticosteroids. A review. Drugs. 1988;36 Suppl 5:51-61.
- Anonymous. Drug Ther Bull 1977: 15: 5–8