It’s always best to try and treat a fungal nail infection before it spreads or causes permanent damage to the nails. A fungal nail infection shouldn't cause any long-term issues in otherwise healthy people once it's been treated, though there's every chance it could recur.
In people who are immuno-compromised because of long term conditions that need regular medication (such as those with diabetes), or people who are having other treatments such as chemotherapy, it’s important that fungal nail infections are picked up and treated promptly. This is because they can lead to other infections that spread and become more serious.