Over the years since the Second World War, we have come to depend on chemicals rather than natural products. Chemicals were more powerful and more easily available. This is nowhere more true than in the sphere of insect repellents. DEET was developed just after the war and developed for use by the United States army for jungle warfare. DDT was used widely on crops around about the same time.
So, you’ve got some time off work, college or school and you want to get outdoors and enjoy it. Maybe even go on holiday. What a good idea! Nevertheless, what happens when you get where you are going? The mosquitoes come out to get you.