ARTICLE: Colloidal Oatmeal Part I: History, Basic Science, Mechanism of Action, and Clinical Efficacy in the Treatment of Atopic Dermatitis

October 2020 | Volume 19 | Issue 10 | Supplement Individual Articles | s4 | Copyright © October 2020


Published online September 21, 2020

Blair Allais MD, Adam Friedman MD FAAD

Department of Dermatology, George Washington School of Medicine and Health Sciences, Washington, DC

Abstract
Colloidal oatmeal has a long-standing history in the treatment of dermatologic disease. It is composed of various phytochemicals, which contribute to its wide-ranging function and clinical use. It has various mechanisms of action including direct anti-inflammatory, anti-pruritic, anti-oxidant, anti-fungal, pre-biotic, barrier repair properties, and beneficial effects on skin pH. These have been shown to be of particular benefit in the treatment of atopic dermatitis. In Part 1 of this two-part series, we will explore the history of colloidal oatmeal, basic science, mechanism of action, and clinical efficacy in the treatment of atopic dermatitis.

J Drugs Dermatol. 2020;19:10(Suppl):s4-7

INTRODUCTION

History of Oatmeal
Oatmeal has a longstanding and rich history pertaining to its dermatologic use. The first documentation of oatmeal for skin health dates back as early as 2000 BC in Arabia and Egypt, where it was described as soothing and protecting in dry or itchy, inflamed skin.1 Oatmeal flour was subsequently recognized as a topical therapy for a variety of dermatologic conditions in Roman medical literature.1 The first scientific studies on the skin benefits of oatmeal appeared in the 1930s, including information about the cleansing properties of oatmeal, its role in relieving itch, and its function as a skin protectant.2 In the 1940s and 1950s colloidal oatmeal became commercially available both in powder form and mixed with emollient oils, instigating medical studies examining the benefits of colloi-dal oatmeal baths in various xerotic dermatoses.3 In 1989, the United States Food and Drug Administration (FDA) approved colloidal oatmeal as a safe and effective over-the-counter drug.4 In 2003, the FDA noted that colloidal oatmeal could relieve irritation and itching due to a number of dermatoses, providing temporary skin protection.5 Colloidal oatmeal is one of the few products that the FDA recognizes as a safe over the counter treatment. Today it is available in various forms including creams, lotions, shampoos, shaving gels, bath treat-ments, and body wash.

Basic Oat Science
Colloidal oatmeal is the powder obtained from the grinding and processing of whole oat grain. Under strict protocols es-tablished by the US Pharmacopeia, oat grain is ground and processed until no more than 3% of the total particles in the powder exceed 150 μm in size and no more than 20% exceed 75 μm in size.6 The small size of the particles contributes to their ability to deposit on the skin and form an occlusive barrier when dispersed in water. Oat is composed of various types of phytochemicals, which contribute to its wide-ranging function and clinical use. Col-loidal oatmeal consists of sugars and amino acids (65%), proteins (15–20%), lipids (11%), and fiber (5%).7 The most important groups of phytochemicals present in oats include phenolics, β-glucans, lignans, avenanthramides, carotenoids, vitamin E, and phytosterols.7 Of the phenolics present in oats, ferulic acid and caffeic acid are strong antioxidants, and fe-rulic acid also has UV absorbing properties.8 Flavonoids, a group of phenolic compounds present in oat, also are capable of absorbing ultraviolet A light from 320–370 nm.9 β-glucans are polysaccharides of D-glucose monomers and have a high viscosity largely due to their β-(1–3)-linkages.7 This viscosity contributes to the water-binding properties of oat. Oats also contain a wide range of minerals and vitamins, of which vita-min E is the most clinically relevant. Vitamin E is a naturally occurring antioxidant that protects against oxidative stress, inflammation, and photo-induced aging.10

Mechanism of Action
Colloidal oat has various mechanisms of action including direct anti-inflammatory, anti-pruritic, anti-oxidant, anti-fungal, pre-biotic, barrier repair properties, and beneficial effects on skin pH. Inflammatory skin disorders including psoriasis and atopic dermatitis (AD) exhibit high levels of arachidonic acid, eicosanoids, phospholipase A2 (the enzyme that mobilizes arachidonic acid), and leukotriene B4, which is a potent che-motactic factor that stimulates neutrophil degranulation and induces keratinocyte proliferation. Oat has been shown to in-hibit phospholipase A2 in keratinocytes, thereby decreasing arachidonic acid release, which decreases pro-inflammatory eicosanoid formation.11 The anti-inflammatory activities of oats have also been studied in the vasculature. Guo et al demon-strated that avenanthramides, specific polyphenols from oats, inhibit IL-1B induced NF-kB activation in endothelial cells.12