Every year. Middle daughter (grade school) is super susceptible with fine straight hair and she is very clean and they soo love clean. Her school every year..Older daughter had a report from a sleep-over a month ago.... Kills our house with 4 girls (I buzzcut). Kudos for gittin-er-dun sober. I've done it twice in the last year and and the laundry alone is 10 hrs.