LYMA Skincare is the most active skin care in existence, which means its highly potent ingredients can react with other products, specifically SPFs containing zinc. For this reason, we recommend using a chemical or titanium dioxide mineral SPF rather than one containing zinc. While this reaction is in no way harmful, zinc can prevent the yellow pigment in LYMA Skincare’s patented Quercetin™ from completely absorbing. This happens because the formula’s patented form of hydrolyzed hyaluronic acid locks in the moisture it has flooded into the skin with an anti-dehydration shield which can result in a yellow residue and pilling of the product on the skin. If you experience this side effect, simply cleanse the skin to remove.