Although treatment is usually sought for cosmetic reasons, nail fungus can be serious and should be treated. For example, if it is a severe infection, it can cause permanent damage to your nails. The infection can also spread beyond your nails, especially if you are in a high risk group, such as people with diabetes or impaired immune systems. High-risk people can develop cellulitis, a skin tissue infection, if toe fungus isn't treated.
If you have diabetes, you may have reduced blood circulation and nerve supply in your feet. You're also at greater risk of a bacterial skin infection (cellulitis). So any relatively minor injury to your feet — including a nail fungal infection — can lead to a more serious complication. See your doctor if you have diabetes and think you're developing nail fungus.