Without treatment, acute gout attacks may develop into chronic gout with destruction of joint surfaces, joint deformity, and painless tophi. These tophi occur in 30% of those who are untreated for five years, often in the outer part of the ear, over the outer part of the elbow, or on the Achilles tendons. With aggressive treatment, they may dissolve. Kidney stones also frequently complicate gout, affecting between 10 and 40% of people. Kidney stones occur due to low urine pH promoting the crystallization of uric acid. Other forms of chronic renal dysfunction may occur.