onychomadesis onychomadesis onychomadesis is a periodic idiopathic shedding of the nails beginning at the proximal end, possibly caused by the temporary arrest of the function of the nail matrix.: 784 : 660 one cause in children is hand, foot, and mouth disease. this generally resolves without complication. onychomadesisspecialtydermatology onychomadesis can also occur if the nail is damaged or has a loss of blood supply; for example, due to a bruise. the nailbed turns black, and the nail drops off shortly afterwards. it takes around 6 to 12 months to regrow.