Thickening hair spray is a cosmetic product that is formulated to increase the perceived thickness of hair strands. In most cases, a thickening hair spray only thickens the hair temporarily, either by coating the strands from the outside or by swelling them from within. In either case, the effects are not permanent, because no structural change to the hair is taking place. Many thickening hair sprays should be used sparingly and applied primarily to the roots of the hair to avoid excess distribution of the product that can weigh down the hair or encourage greasiness.
The general purpose of a thickening hair spray is to act as a hairstyling aid. These products are intended for daily use and will not produce a long-term thickening of the hair itself. The hair is being only manipulated and not altered in composition, so when an individual stops styling his or her hair with a thickening hair spray, he or she will most likely not notice lingering results.
In general, there are two ways that a thickening hair spray can achieve the desired results. First, the spray could contain polymers or other ingredients that coat each outside of the hair shaft, which gives the temporary illusion of thicker strands. Second, the hair spray could contain ingredients that penetrate the hair cuticle and encourage swelling of the shaft from within. In this instance, the results include hair that appears to be thicker than it is naturally.
Some formulas of thickening hair spray tend to be somewhat sticky or tacky, and they depend on blow drying and styling to activate the ingredients to their full potential. Products of this nature are applied to the roots of the hair. The hair is then blow-dried as the stylist lifts it away from the scalp, so that when the hair is dry, it has more height and volume. Adding volume at the roots is another way that thickening hair sprays give the illusion of thicker hair.
Many people who employ thickening hair sprays do so because their hair is naturally thin and fine. These hair types are susceptible to greasiness and flatness if products are applied with a heavy hand, however. Therefore, it is very important to use thickening hair sprays sparingly and to use them only in strategic locations such as right near the roots. It also is wise to isolate thickening sprays to the roots because these products can make fine hair feel dry and brittle if it is applied over the middle and ends of the hair.