Developments in guar derivatives and boric acid

The current situation may be considered a period of transition wherein the different industries assess the risks associated with boric acid and borates and policies are developed. There are certain oddities, such as the continued listing of boric acid and borates as a food additive up to a level of 0.4% in caviar in the EU (EC 1129/2011). For most industries, however, the reaction was quick or even pre-emptive and the presence of boric acid in many consumer products has been limited or its use has been eliminated altogether – examples include toys, cigarette paper, carpets and other textiles. But what were the consequences in the cosmetics industry? This article does not seek to provide a complete overview on boric acid in the cosmetics industry. Instead, the developments shall be illustrated on the case of guar derivatives.

Guar derivatives

Guar derivatives are commonly used in the cosmetics industry as rheology modifiers, stabilisers or conditioning polymers. Traditionally, guar derivatives such as hydroxypropyl guar and guar hydroxypropyl trimonium chloride contain boric acid and borates. The reason is two-fold. Firstly, borates have been used in the production of these guar derivatives as processing aids, facilitating a specific route of production. Secondly, borates provide a very specific functionality to guar gum and its derivatives. The complexation of the metaborate-ion (B(OH)4-) by monosaccharides results in a cross-linking between the polysaccharides that constitute guar. This cross-linking retards or inhibits the swelling of guar at alkaline conditions. By lowering pH the cross-linking is broken as the metaborate ion is converted to boric acid and rapid swelling may be induced. This effect proved very useful in processing guar derivatives, as it allows for trouble-free dispersion of guar derivatives without formation of lumps at alkaline pH and rapidly induced swelling in a second step. The concentration of boric acid and borates in guar derivatives is usually low, e.g. 1%. Considering the usual application concentration of guar derivatives in cosmetic formulations, e.g. typical levels of guar hydroxypropyl trimonium chloride in conditioners are around 0.2% to 0.4%, then the concentrations of boric acid and borates induced from guar derivates as carry-over into the final product were well below 100 ppm. Consequently, one would have to absorb the boric acid and borates of about 0.5 kg of final product per kg of bodyweight in order to reach reported NOAEL (No Observed Adverse Effect Level) values. Given that dermal absorption through intact skin is very low, it is obvious, that these levels have not prompted widespread concern. Nevertheless, increased scrutiny with regards to boric acid and borates and perceived reputational risks associated with their use, however, have led to ambitious efforts to eliminate it from guar derivatives. All major suppliers of guar derivatives for the cosmetic industry now offer ‘boron free’ variants of their products, which offer the same functionality.