The negatives of this system are that these formulas are often greasy because of the presence of the polymer, and they re less effective than the Controlled Release system. By working together they each become more effective, last longer, and absorb less into the skin than straight deet formulas. A simple rule is to look for three names you cannot pronounce on the label and not just one. Due to convenience most repellents are applied in a spray format. Alcohol can also open skin pores and promote deet absorption.
Water based and low percentage alcohol formulas are better.
These formulas work best on clothing but are only effective on skin for short periods. Recent adverse publicity has left many people confused and concerned about the safety of deet. Although deet does not create a skin sensitivity it is a skin irritant. This means that after a period of frequent and repeated use your skin may become red, even sore to the touch. While your skin will recover between uses, each subsequent use could again display irritation.