Some cucumbers have bitter-tasting skin. The bitterness comes from a compound found in cucumbers and similar plants called curcubitacin. Weather patterns, age at harvest, and other factors can increase the bitterness in cucumbers. Dry growing conditions, nutrient-poor soil, and lack of sun can produce a thick, bitter peel. For this reason, you might have better luck finding sweet cucumbers from a local, organic grower at your farmer's market than at the grocery store.