Hard Water and Skincare

Hard water significantly impacts skin health, contributing to various issues including an increased risk of atopic eczema (AE), higher prevalence of eczema and xerosis. Mineral ions in hard water react with soap fatty acids to form insoluble metallic soap, disrupting the skin barrier. Hard water exacerbates dryness and redness, reduces hydration, and directly impacts the skin by disrupting its natural epidermal gradient, affecting keratinocyte differentiation, inhibiting epidermal repair, and disrupting the bilayer lipid water barrier.

Hard water’s alkalinity and buffering capacity can modify skin surface pH, altering epidermal enzyme activity, which is pH-sensitive and crucial for barrier function). In terms of strength and elasticity, hard water mineral deposits can increase hair porosity and brittleness, making it more susceptible to breakage, especially when wet or during styling. The surface of hard water treated hair has a ruffled appearance with higher mineral deposition and decreased thickness when compared with the surface of distilled water treated hair. Hard water decreases strength of hair and thus increases breakage. Besides skin and hair health, hard water presents a significant challenge in various applications, including the effective use of cosmetic products. The elevated levels of these minerals can interfere with the intended function of soaps, face cleansers, shampoos, conditioners, and other personal care items, potentially diminishing their efficacy and altering their sensory attributes.

In the cosmetics industry, lather, or foam, plays a significant role in the user experience and perception of product effectiveness, though it is not a direct indicator of cleansing ability. A good lather enhances the sensory experience, making products feel more luxurious and effective. Liquid foams are colloidal systems in which a discontinuous gas phase is dispersed in a continuous liquid phase, giving rise to a multitude of gas bubbles. These bubbles can be either closely packed together forming the characteristic “cellular structure” of the foam, or float freely in the liquid. Much of the usefulness and appeal of liquid foams lies in their rheological properties. (Rheology is the science of how materials deform and flow under applied forces). They combine the properties of an elastic solid at low stress with those of a liquid when the yield stress is exceeded. Hard water can significantly impact the foaming properties of cosmetic products by reducing foamability due to the precipitation of surfactants.

The impact of hard water on foam in cosmetic applications has significant implications for product development and cosmetic manufacturers must consider the water quality in target markets when formulating products. For example, in regions with hard water, formulations may require higher surfactant concentrations or the use of surfactant blends to maintain desired foam properties. High ionic strength generally acts to destabilise both surfactant-stabilised foams and charged colloidal systems by screening electrostatic repulsions, leading to thinner films and faster drainage in foams, and increased aggregation in colloids. Given these well-documented detrimental impacts of hard water on skin and hair health, and its pervasive presence in many regions globally, it is critically important for the cosmetics industry to understand how its products interact with such water conditions. Consumers in hard water areas rely on cleansing and care products to maintain skin and hair health, and if these products themselves are compromised by water quality, their intended benefits are diminished.

The presence of hard water ions fundamentally weakens the internal foam structure, leading to accelerated bubble coalescence, increased liquid drainage, and a critical loss of elastic, solid-like mechanical properties, causing the foam to behave more like an unstable liquid. This multi-faceted approach encompassing macroscopic, microscopic, rheological, and tribological analyses provides a robust and unprecedented understanding of this widespread phenomenon.

This fundamental insight is invaluable for developing next-generation cosmetic products that deliver consistent efficacy and superior sensory attributes in diverse global water conditions, ultimately enhancing consumer satisfaction and minimising product waste due to poor performance. These findings also emphasise the critical importance for researchers to consider water quality, particularly hardness, when developing cleansing products to ensure optimal product efficacy. Additionally, leveraging foam boosters and rheology modifiers can enhance foam stability and integrity to ensure consumer satisfaction and product performance across diverse water qualities.

Not my own work. Taken from: (any Italics are mine)

Mehta, R.; Paul Choudhury, R. Cosmetic Foams: The Rheo-Tribological and Microstructural Effects of Hard Water. Cosmetics 2025, 12, 270. https://doi.org/10.3390/cosmetics12060270

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