Repellents are products that prevent mosquitos from biting you. These substances consist of concentrations that are safe on bare skin.
A product like permethrin, on the other hand, effectively kills mosquitos and other insects like ticks. It’s very concentrated, and you should never apply it to your skin. However, it’s safe to use as long as you follow directions on the label.
You can use DEET on your skin if the concentration isn’t higher than 50 %. Otherwise, it’s recommended for use on clothing or gear only as it’s becoming too concentrated without further increasing the duration of protection. Keep in mind, however, that DEET can cause damage to synthetic materials like clothing and glasses.