Sometimes a callus occurs where there is no rubbing or pressure. These hyperkeratoses can have a variety of causes. Some toxic materials, such as arsenic, can cause thick palms and soles. Some diseases, such as syphilis, can cause thickening of the palms and soles as well as pinpoint hyperkeratoses. There is a benign condition called "keratosis palmaris et plantaris", which produces corns in the creases of the fingers and non-weight bearing spaces of the feet. Some of this may be caused by actinic keratosis, which occurs due to overexposure to sun or with age and hormonal shifts.