Garlic can cause both+(depends on the strength, form and amount of garlic being used as well). Garlic contains many sulfur compounds. Some research indicates that the sulfur compound (1, 2-vinyldithiin) has some anti-inflammatory properties. But the burning like properties of sulfuric acid and allicin( if not properly nuetralized) is going to further irritate and inflamme tissue. Especially if someone already has inflammation present in the gut. For people that already have a inflammed Gi tract fresh or raw garlic is a bad idea. Odorless aged garlic is a much better choice for people that have a sensitive GI tract.