Leather does that. To clean it get some warm water and a sponge,wring the sponge out and wipe the leather over, dont get it to wet.
Is it soft leather or thick like a belt ?
To keep it supple use Carr,Day and Martins glycerine saddle soap, use another dry sponge and wet the bar of saddle soap rub it on the sponge and apply to the leather,if you wet the sponge to much you will end up with foam everywhere.
The only way to stop leather from going mouldy is to clean it regularly.
Other good ones are Jefferies saddle soap and Ko-cao-line which is a leather dressing.