How long does bug spray stay on surfaces?
DIY insect surface spraying safety tips
Effectiveness—Insecticide surface sprays may last from 4 weeks to 3 months. You will need to know how often to re-spray to maintain the protection.
What happens if you don't wash off DEET?
Very often, people don't wash the product off their skin after returning indoors. This can result in overexposure, especially in cases where a product is applied too often (at short intervals) or daily for several days. A small amount of DEET is absorbed into the body when applied to the skin.