The reason there are theories that wheat causes acne is because wheat products can alter the glycemic index (GI) which provides a measure of how quickly blood sugar levels rise. All high GI products eg. white bread, most white rice, corn flakes, extruded breakfast cereals, glucose, maltose, maltodextrins, potato, sweets etc, cause blood sugar to spike dramatically. Elevated blood sugar stimulates your body to pump out insulin which then triggers a cascade of hormonal effects, including elevated levels of androgens (the acne-causing male hormones), excess oil, and increased skin cell production, all of which lead to clogged pores and breakouts. Also, some cases of acne (and eczema, psoriasis) are aggravated by food allergies, eg. gluten which is found in such grains as wheat, barley and rye.