This is a 2018 meta-analysis in the Journal of Travel Medicine comparing DEET against picaridin for mosquito repellancy:
academic.oup.com
This study does not evaluate or balance the supposed "side effects" of DEET and picaridin. The following 2021 product ranking article seems to give great weight to picaridin because DEET "smells bad, feels oily, and can damage plastic and synthetic fabrics."
www.nytimes.com

Mosquito repellents for the traveller: does picaridin provide longer protection than DEET?
AbstractBackground. This review examines the published laboratory and field tests where the repellents DEET and picaridin have been compared for their effi

There was not a consistent difference in performance between DEET and picardin in field studies. In two studies picaridin appeared to outperform DEET, in two studies DEET appeared to outperform picardin, and in four studies these active ingredients performed equally well. It is, however, noteworthy, that in the two studies where DEET appeared to provide enhanced protection, the concentration of active ingredient in the tested DEET product was substantially higher (~1.5 or 8 times) than in the tested picaridin product.
In conclusion we feel that where 50% DEET products are available then it can be argued that the protection time advantage associated with these formulations reasonably can be invoked to consider it as a first choice repellent. Where only 30% DEET or lower concentrations are available, then on current evidence it is reasonable to offer DEET or picaridin as a first choice.
This study does not evaluate or balance the supposed "side effects" of DEET and picaridin. The following 2021 product ranking article seems to give great weight to picaridin because DEET "smells bad, feels oily, and can damage plastic and synthetic fabrics."

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