The aloe is an extremely hardy plant and can tolerate harsh conditions that other plants cannot. Since it is a type of cactus (succulent), 90 percent of an aloe's mass comes from water stored in its leaves.
Aloe is susceptible to a type of fungal disease which causes a dark soot like substance to appear on the leaves of the plants. This often happens to young plants have been damaged or to plants that are frequently over watered. Allowing the soil to dry out will alleviate this problem.
Aloe plants kept in conditions that are too cool or damp are at risk for developing basal stem rot. The stem of the plant starting at the soil become dark red or blackish in color and begins to rot. Grafts can be taken from healthy parts of the plant and rerooted. Afterwards, the diseased plant is generally disposed of.
When water is allowed to stand on the leaves of the plant, the leaf walls can break down and allow bacteria to enter the plant causing dark rust colored spots to appear on the leaves. Leaf spot does not typically kill aloe plants unless rot sets in. Trim the infected leaves away, and do not allow water to collect on the surface of the plant.
Most diseases that afflict aloe and other succulent plants are caused by over-watering. Aloe plants are native to dry climates and do not need frequent watering.
Aloe is often referred to as the world's most powerful moisturizer. In fact, many skin care products are made from the clear gelatinous pulp found inside the aloe vera leaf.