Shellac may save money in the short run, however the damage caused by the harshness of the polish could last a very long time. Due to the strength of the chemicals in each shellac coat, removing the color is a very harmful process. The nails must be soaked in pure acetone for 10-15 minutes to soften the color, followed by manually scraping the nails with a metal tool. In a study done by the Journal of Cosmetic Dermatology, they observed the thickness of the nails of 5 different women before and after shellac manicures. Before the gel polish was applied, the average thickness of the left thumb was 0.063 cm. After removal of the gel polish, nails were noticeably thinner and more brittle and averaged a thickness of 0.050 cm. This is a significant drop in nail thickness.
This study also found that it was unclear whether it is the harsh chemicals in the coats of gel polish or the removal process that causes such damage to nail health. However, the removal process is inevitable at some point after applying gel polish so it is difficult to clarify this gray area.
Shellac manicures are great in that they look fresher for a longer period of time, but it is to each their own when it comes to deciding if the fresh appearance is worth the real underlying damage.