Sodium Borate

Sodium borate (borax) is an alkaline buffering/cleaning salt; in leave-on or rinse-off products its higher pH and salt nature can disrupt the stratum corneum and sting compromised skin, especially in eczema. Patch-test and occupational data show it can be irritating to skin and mucosa at relevant exposures, even if it is not a common true allergen. Given sensitive-skin populations and cumulative routine use, I rate it as a moderate irritant where irritation is plausible and patch testing is prudent. Safety Notes: In modern OTC cosmetics, sodium borate (borax) is most often present at very low levels (around 0.01–0.3%) as a pH adjuster/buffer or formulation aid in rinse-off products (soaps, cleansers) and some leave-on items where permitted. Higher concentrations exist in consumer-available niche products that function more like topical antiseptic/astringent or powder-to-solution preparations (and some legacy formulations), where borate salts can reach low single-digit percentages; above ~5% is uncommon in mainstream skincare due to sensitization/irritation risk and tighter boron-related regulatory scrutiny (notably in the EU, which restricts/limits boron compound use depending on product type and exposure).