Water hardness varies up to 17-fold across major Latin American cities (Belém 18 mg/L vs. Mar del Plata 320 mg/L). This technical note proposes and justifies the elevation of water hardness to an independent eighth dimension in the Cutaneous Exposome Index (ICE-8™), calibrated for Latin American populations. Hard water is associated with TEWL +25%, cutaneous microbiome disruption via pH shift, and reduced cleansing efficacy — mechanisms absent from all existing exposome frameworks.
Willer de Souza (2026) studied this question.