How often do I need to change baby's bedsheets?

Try to wash at least once a week. Babies may be exposed to dirt around the house as they crawl around to explore their surroundings. Instead of specific baby laundry detergent, you can consider the Ecover Zero series that is formulated for people with sensitive skin (we often neglect that chemicals from the laundry detergent may linger on the clothes and may be too harsh for sensitive skin). http://ecover.com.sg/collections/laundry/products/zero-laundry-liquid