Lemon just got checked.
The fruit shows a rough, corky, scabby rind rather than soft rot, which fits citrus scab best. This is usually a fungal or fungal-like fruit-skin disease that damages the peel while leaving the inside largely usable. The leaves look mostly healthy, so the problem appears focused on the fruit surface rather than the whole tree. Since you said it’s getting worse and the skin is scabby, this is more likely scab than nutrient burn or rot.
What to do today
This is usually a cosmetic-to-mild fruit disease. Focus on stopping spread and protecting new fruit.
Also possible, but less likely
What would prove it
Watch for spread on new fruit
Check new fruit for fresh raised corky spots. If the tree is making new scabby fruit quickly, consider a citrus-safe preventive program for next season rather than trying to fix the current fruit.
Turn this into a recovery case
One photo gives a diagnosis. Tracking proves whether the plant is recovering.
Don’t leave the diagnosis hanging 🌱
Save it now, then use the next photo to confirm if this was the right call.
Create account & save plant 🌱