Mosquito repellents come in a lot of shapes and sizes: aerosols, creams, lotions, & sticks. There's even mosquito repellants built into some clothing. Most skin repellants contain deet, which can last a few hours but will need to be re-applied afterwards.
Citronella oil is commonly used in candles, torches and mosquito coils. It creates mosquito-repelling smoke. It is an effective mosquito repellant in high concentrations. It should be noted, however, that individual citronella-producing plants do not make enough oil to effectively repel mosquitoes.
Use repellants correctly and wisely to ensure safe and effective results. Always read the label before applying any mosquito repellent. Apply as directed to clothing or exposed skin and never exceed the manufacturer's recommended application amount or frequency.