DEET can cause skin irritation in some people, but this is rare. Some people who have used high strength DEET or had exposure to DEET over a long period have experienced adverse effects. DEET is also toxic if ingested.

While DEET is an incredibly effective insect repellent, many people choose to avoid it due to concerns regarding its chemical intensity and potential side effects. DEET (N,N-Diethyl-meta-toluamide) is a powerful solvent that can damage or melt synthetic materials, including plastic watch faces, eyeglass frames, and technical fabrics like spandex or rayon. From a health perspective, some users report skin irritation, rashes, or a greasy, unpleasant sensation upon application. In rare cases of heavy over-exposure, particularly in children, it has been linked to neurological concerns such as dizziness or headaches. Furthermore, DEET has a distinct, pungent chemical odor that many find off-putting in nature. In 2026, many travelers are pivoting toward "Bio-Rational" alternatives like Picaridin or Oil of Lemon Eucalyptus (OLE), which offer similar protection times against mosquitoes and ticks without the "plastic-melting" properties or the harsh chemical footprint of traditional DEET-based products.