Summary of Scientific Research
There is no solid evidence of coffee grounds being able to repel mosquitoes, but during the Zika virus outbreak in 2016, some websites claimed coffee grounds as the best option.
However, there is some evidence of burnt coffee grounds, along with caffeine, inhibiting the growth of mosquito larvae.
Be careful though, as mosquito larvae could potentially benefit from the introduction of coffee grounds.
The reason coffee grounds are able to inhibit larvae growth is the caffeine it introduces. Caffeine has different effects depending on the insect it is introduced to. For mosquitoes, caffeine prevents mosquitoes from swimming up to the surface, killing them before they can become adults.
Rubbing coffee grounds over your skin won’t hurt, but it won’t help either. But if you can track down the location of where the mosquitoes are breeding, you can at least delay the growth of future pests, if not outright killing them.
Being able to control the population is a step up from letting a mosquito infestation happen, but be warned that the study only tested coffee grounds with the mosquito species Aedes aegypti. Also, another study claimed that coffee grounds could act as nutrition for some larvae. If you don’t know the type of mosquito that’s around your house, you may not want to risk it, especially if your area is in dire need of a good repellent.
How to Use Coffee Grounds as a Mosquito Repellent
You can get coffee grounds at any local grocery store or chain like Target or Walmart. Remember, we’re talking the actual coffee grounds that you put in a filter and brew — not K-Cups or instant crystals/powder.
Once you’re done making that sweet cup of coffee, take the burnt coffee grounds to the area of mosquito larvae. It’s up to you whether you use recently-used coffee grounds or week-old coffee grounds(some sites say to use one or the other). Once spread around, the larvae will either stop developing or get a free meal. It’s a risky move, but one worth taking.
If you only have a minor mosquito problem and can’t be bothered to spend money on a couple of pesky mosquitoes, then using your coffee grounds won’t hurt. However, you’ll need to know where the larvae are, and locating larvae can be pretty difficult.
Or, you could just pour coffee grounds into every source of water you have, hoping to catch the larvae. I don’t recommend it, but you could!
Other Household Items as Mosquito Repellents
Checkout our analysis of other household items as natural mosquito repellents: