Provided you eat a balanced diet, chocolate won't give you spots.
However, recent studies show that diet does have some influence, although fatty foods, which have always been thought to be a culprit, don't actually cause acne. This is a problem that rarely occurs among native populations with diets rich in fat, such as the Arctic Inuit. In the western world, however, acne is a widespread skin complaint, and members of native populations don't usually develop it until they move into a modern city.
Evidently, western eating habits can encourage skin impurities. Scientists suspect that a diet rich in simple carbohydrates is the indirect trigger for acne. The consumption of large amounts of sugar leads to a continuous release of insulin, which creates a shift in the hormonal balance and thereby stimulates the production of sebum.
This would seem to suggest that chocolate does at least encourage spots, particularly the high-sugar, low-cocoa varieties. However, chocolate won't do any harm to those whose diet is based on complex carbohydrates and small amounts of sugar and white flour.