Issue link: https://www.ascpskindeepdigital.com/i/1545716
32 ASCP Skin Deep Summer 2026 How Humidity Shapes Skin Health by Shawna Rocha GETTY IMAGES SKIN PHYSIOLOGY HUMIDITY IS A CRITICAL ENVIRONMENTAL factor that directly infl uences skin physiology, barrier function, and overall skin health. Variations in relative humidity (RH) can signifi cantly alter transepidermal water loss (TEWL), lipid organization, enzymatic activity, and microbial balance. Understanding how diff erent humidity levels aff ect the skin provides valuable insight for treatment strategies and product selection in clinical and professional settings. LOW-HUMIDITY ENVIRONMENTS (BELOW 30 PERCENT RH) Low-humidity conditions, commonly experienced in winter climates or climate-controlled indoor environments, create a strong gradient for water evaporation from the skin. This leads to increased TEWL, where water passively diff uses from the deeper layers of the epidermis to the external environment. As TEWL increases, the stratum corneum becomes dehydrated, resulting in reduced elasticity, impaired barrier integrity, and a compromised lipid matrix. Intercellular lipids— primarily ceramides, cholesterol, and free fatty acids—become less organized, weakening the barrier's ability to retain moisture and defend against external stressors. Low humidity also impacts desquamation, a term for the natural shedding process of corneocytes. Enzymatic activity responsible for corneocyte separation becomes less effi cient in dry conditions, leading to corneocyte retention, visible fl aking, and rough texture. Clinically, this presents as dryness, dullness, increased sensitivity, increased reactivity, and a heightened risk for skin conditions such as eczema, psoriasis, rosacea, and dermatitis. Additionally, low-humidity environments can infl uence sebaceous gland activity. While sebum production may not necessarily increase, the perception of dryness often leads to compensatory overuse of occlusive or emollient products, which may disrupt the skin's natural balance if not appropriately selected. Treatment Considerations in Low Humidity In low-humidity environments, the focus should be on barrier repair, water retention, and lipid replenishment. Nonstripping, sulfate- free cleansers are essential to avoid further disruption of the barrier. Treatments should incorporate rich moisturizers and occlusives that reduce TEWL and deliver sustained hydration and lipid support. Layering humectant serums (such as hyaluronic acid in multiple molecular weights) with barrier-supportive ingredients like