Occasionally I'll get a clove of garlic that has small brown spots on it. When there are a couple spots, I cut them off and use the rest of the garlic. Sometimes there will be A LOT of spots and clustered together. Those will get thrown away. The garlic will look and feel fine until I remove the white "skin." It really looks like the garlic has eczema or measles. Does anyone know what these spots are? Is this a form of garlic mold?
The brown spots can be a bruise from handling or a bruise caused by heavy soil. We learned the hard way to avoid planting in heavy clay. Loads of brown spots from cloves trying to swell against hard soil, or a rock or buried root etc. The bacteria get into the bruised clove and quickly discolour it.
We added lots of compost and tried to make our garlic patch soil the lightest, fluffiest texture possible. The softest soil produced the cleanest bulbs. Also far less bruising from harvesting since they pull so easily out of the ground.
Most of the websites I found say that the brown spots are a sign of the garlic going bad. The excerpt below from wikihow echoes what most say about it.
Check over the clove for any brown spots. Usually if a small spot you can trim off and the garlic is still good. If two or more spots, just pitch it in the trash can and get another clove.