The pores in the lemon rinds allow moisture to escape the fruit, causing it to dry out and go bad.
To keep the lemons fresh longer, put your lemons in a bowl of water and put it in the fridge. Alternatively, you can put lemons in an air-tight plastic bag in the fridge.
The water in the bowl serves to replenish the lost moisture to the lemons, and the plastic bag serves the same purpose of maintaining the moisture within the fruit.
