Bottles Turning Yellowish

Is it OK to continue using the bottle if it turns yellow? Only been using for 2.5 months and it turned yellow. Using Dr Brown's currently. Suspect its due to the heat from uv sterilizer as I have tendency to reheat the empty bottles in them after every wash of every other bottles. Currently lo has 7 bottles which I wash all at once at the end of the day. But sometimes when has some free time, will washed a few first and put it in to the sterilizer to sterilize and heat to dry together with the rest of the bottles that has been dried and sterilised. Is that OK? Will it cause any chemicals to seep out from the bottles or something?