The effects of hard water on the skin.

Hard water, also known as calcareous water, is a type of water naturally rich in minerals, primarily calcium and magnesium. This composition results from prolonged contact with limestone or dolomite rocks as it seeps into the ground before reaching the water table. The higher the mineral concentration, the harder the water is considered. While it can leave whitish traces on surfaces or make laundry feel rougher, it poses no health risks. On the contrary, it provides an additional source of calcium and magnesium, two essential elements for the body's proper functioning.

However, on the skin, very hard water can slightly weaken the hydrolipidic film, leading to feelings of dryness or discomfort, especially in individuals with sensitive skin.

Hard water is notably associated with a higher risk of xerosis, that is, extreme skin dryness. This is what a recent Danish study with over 10,000 participants has shown. The precise chemical mechanism is still debated, but an irritative component is suspected by the researchers of the study. The calcium present in hard water tends to reduce the soap's ability to foam, thereby encouraging the use of a larger amount of product and more vigorous skin scrubbing. However, these mechanical aggressions weaken the skin barrier, leading to a loss of hydration and increasing the epidermis's permeability to irritants.

Some studies have also shown that hard water was associated with skin conditions, such as contact dermatitis. One of these, conducted with over 300,000 participants, highlighted that exposure to hard water, with a concentration of CaCO3 above 200 mg/L, increased the risk of eczema by 12%. For your information, depending on the municipalities, tap water in France has concentrations of CaCO3 ranging from 0 to 400 mg/L.

Indeed, hard water alters the calcium signalling within the epidermis, thereby disrupting the renewal of keratinocytes and weakening cellular cohesion. Calcium signalling follows a natural gradient within the epidermis: its concentration is lower in the basal layers where cells proliferate and higher in the upper layers where they differentiate and ensure the formation of the horny layer. Water rich in calcium could disrupt this balance and the maturation of keratinocytes, leading to a less effective epidermal barrier. Furthermore, calcium plays a role in the adhesion between the cells of the epidermis via cadherin proteins. An alteration of this signalling could weaken cellular cohesion, thus promoting irregular desquamation and an increase in skin permeability, two factors that could exacerbate conditions such as eczema.

Another effect of hard water is the reduction in soap solubility. In the presence of a high concentration of calcium and magnesium ions, soap forms insoluble residues that adhere to the skin after rinsing. These deposits, by remaining on the skin's surface, can disrupt its balance, particularly by altering its pH and limiting the absorption of subsequent treatments. This can lead to a feeling of discomfort, promote irritation and, in reactive skin, trigger inflammatory reactions.

Finally, hard water is suspected of accelerating skin ageing. Certain impurities present in hard water, such as iron or magnesium, can form free radicals, reactive species that can alter cell membranes, lipids and structural proteins like the collagen and elastin. This oxidation process leads to a degradation of the skin structure, impacting the suppleness and elasticity of the skin while accelerating the formation of wrinkles.

Good to know : The installation of a water softener, a device designed to filter calcium and magnesium crystals, can neutralise the effects of hard water on the skin. Rinsing your skin with thermal water can also be a solution. However, while it is suitable for the face, it may be a bit too restrictive for the entire body.