Do coffee grounds repel mosquitoes?

Do coffee grounds repel mosquitoes is popular DIY myth, but scientific evidence shows coffee grounds have very limited effectiveness as mosquito repellent and should not be relied upon for significant protection. The myth suggests that burning coffee grounds creates smoke that repels mosquitoes, or that sprinkling dry coffee grounds around yard repels them due to strong smell, or that coffee grounds in standing water kill mosquito larvae. Some anecdotal reports claim burning coffee grounds like incense produces smoke that repels mosquitoes similarly to citronella, because smoke itself repels mosquitoes regardless of material burned, as mosquitoes dislike smoke. However, studies on coffee grounds as larvicide show mixed results, with some lab studies indicating coffee grounds in standing water may deter female mosquitoes from laying eggs due to caffeine toxicity, but concentration required is high and not practical for large water bodies. EPA does not register coffee grounds as insect repellent, and CDC does not recommend them. Effective methods for repelling mosquitoes include EPA-registered repellents containing DEET, picaridin, oil of lemon eucalyptus, removing standing water, using barrier sprays with pyrethroids, and using fans. Coffee grounds may provide very slight repellency when burned due to smoke, but same effect can be achieved by burning any material, and it does not provide residual protection or kill mosquitoes effectively. So coffee grounds alone do not reliably repel mosquitoes.