Succulent plants, such as the aloe vera, store water in their leaves and roots. This plant also contains a healing gel inside the leaves which can be applied to sunburns and insect bites.
Too much water will cause the roots to rot which results in the roots not being able to supply water to the plant. In the beginning stages, the leaves will plump up and appear healthy. However, as the roots rot and deteriorate, they cannot supply sufficient water. The root-rot will continue into the leaves, turning them yellow and soft, and eventually kill the plant. If the soil always seems to be wet, remove the plant from the pot and examine the roots. If the roots have not died, do not water until the soil starts to dry.
Check the plant for aphids. Aphids are covered with white, fuzzy looking wax. The pest feeds at the base of the leaves and will cause yellow, wilted looking leaves that tend to roll inward the length of the leaf.
Insufficient lighting will cause yellow, stunted and thin leaves. Spaces will also develop at the leaf joints. Fix this by placing the plant in a sunny location; however, too much light will result in scorching. Experiment with different locations until the aloe vera plant is healthy.