Iodine

Research suggests that too much iodine can cause an acneiform eruption, skin problems including acne vulgaris, acne rosacea, folliculitis and perioral dermatitis. These effects may include (severe) allergic reactions, soreness of teeth and gums, intestinal upset such as diarrhea, rashes and other skin problems, depression, inflammation of the salivary glands and thyroid problems.

Side Effects of Too Much Iodine. References from: http://www.healwithfood.org/side-effects/iodine.php