Aloe vera plants can turn brown due to sunburn, fungus or bacteria. The plant may be getting too much sunlight or the soil may be too wet.
Sunburn will make aloe vera leaves turn dry and brown. Mushy brown leaves indicate a fungus, such as basal stem rot, which occurs in the cold and damp. Aloe rust thrives in high humidity and causes brown spots that spread. Bacterial soft rot develops in high humidity and wilts the leaves.
To prevent browning, aloe vera plants should be allowed to dry thoroughly between watering. These succulents need bright sunlight that is not overly strong. The best way is to place them near a sunny window with low humidity.