A tingling or cooling sensation signals penetration of a product and dissipates quickly after initial application. A slight, temporary flush may occur that transforms rapidly into a rosy glow. Reactions with iS Clinical® products are extremely rare but a reaction to any product is possible. If the immediate sensation fails to dissipate over a few minutes, or if flushing persists or increases, a reaction could be present. We recommend consulting with your skin care professional about these effects.