Elemental iodine is an oxidizing irritant, and direct contact with skin can cause lesions, so iodine crystals should be handled with care. Solutions with high elemental iodine concentration such as tincture of iodine are capable of causing tissue damage if use for cleaning and antisepsis is prolonged. Although elemental iodine is used in the formulation of Lugols solution, a common medical disinfectant, it becomes triiodide upon reacting with the potassium iodide used in the solution and is therefore non-toxic. Only a small amount of elemental iodine will dissolve in water, but triiodides are highly soluble; potassium iodide thus serves as a phase transfer catalyst in the tincture.  This allows Lugols iodine to be produced in strengths varying from 2% to 15% iodine.
Elemental iodine (I) is poisonous if taken orally in large amounts; 2–3 grams is a lethal dose for an adult human. 
Iodine vapor is very irritating to the eye, to mucous membranes, and in the respiratory tract. Concentration of iodine in the air should not exceed 1 mg/m (eight-hour time-weighted average).
When mixed with ammonia and water, elemental iodine forms nitrogen triiodide, which is extremely shock-sensitive and can explode unexpectedly.