My well established lemon tree has leaf curl and the fruits have spotted skins.
Ailing Lemon Tree
Certified GKH Gardening Expert
It sounds like the tree has a pest, maybe scale or aphids. It is hard to say as there are several pests that cause this kind of damage. We recommend treating these kinds pest with neem oil. It is safe for humans and animals but is very effective against most destructive plant pests.