Pemetherin is applied to clothing. it wears off due to abrasion or washing. It breaks down quickly on skin so do not waste it trying to apply it to skin. Ticks nornally transfer from the underbrush by latching onto whatever is nearest to them and to them the permethrin is a contact insecticide so they do not latch on. You also can soak clothes with it, which is what the military does or there is service you can send clothing to to have applied. These treatments last longer. Many people buy concentrated permethrin, dilute it down and use a spray bottle to apply it to clothing.
Permethrin Soak Method Guide. If you apply it to gaiters and pant legs, they rarely make it to the legs. They will hide in crevices of boots and creases in socks (if not treated). It does not affect plastic.
Deet can be skin applied, it is an industrial plastics solvent. People think that applying 100% Deet is better at lower concentrations, that is wrong, its best applied in the 30% range. Think of it as perfume or cologne, a little dab will do it. The product I use is 3M Ultrathon, it has a few added ingredients that make the DEET last longer by keeping it from absorbing in the skin. DEET is less effective with ticks than permethrin, but it can be applied to skin. At 100% concentration, it will try to dissolve most plastics with no benefit. BTW, DEET has been researched many times by various agencies and its safe when used properly for adults. It is not rated for children due to lack of research.
I will not use picaridin due to its severe side effect if inadvertently. introduced into the eyes. Just too easy to transfer it to the forehead and have bit of sweat bring it into the eyes. It effects last 12 to 24 hours in my case.