Making white clothes white again has long bedevilled those doing laundry. Some new approaches, and one old one, are likely to restore stained or spotted white clothes to their original whiteness. You may need to take more than one approach, but success is within your reach.
Take action as quickly as you can. Keep the soiled area wet until you can work on it. If your spot contains fats or proteins (lipstick, spaghetti sauce, ice cream, blood), use cool water and rub with a bar of soap, followed by liquid dish detergent. If the stain is mostly colour (fruit juice, grass-stain or wine), use hot water. Often you'll succeed right away. If so, wash and dry garment as usual -- assuming your clothing is washable.
Use enzyme-based presoak, according to directions, and wash the garment in warm water with non-chlorine bleach added to detergent if some stains remain. Sometimes a recent tough stain will require two rounds of this. Most importantly, do not put the garment in the clothes dryer until your stain is out. Heat from the dryer can "set" the stain.
Treat the stain cautiously if the origins of the stain or the fabric content of clothing -- or both -- are in doubt. Take the clothing to a dry cleaner (if you find make-up on a pastel fuzzy sweater, for example). The garment may or may not need to be dry-cleaned, but a second opinion from someone experienced in stain-removal and fabrics can add to your strategies or help you decide how far to experiment on your own.
Remember that old fabrics often respond best to old methods. Try a bar of plain soap with water, then move on to lemon, salt, and sunshine. Line- or air-dry to check results.
Dampen clothes to be whitened with lemon, salt and sunshine. Pour lemon juice (473 ml -- 2 cups -- or more) in the bowl and add 273 g (1 cup) of salt; stir to dissolve. Put dampened clothing in bowl, soaking up all juice mixture. Hang the garment outside in the sun for at least 6 hours or all day until dry and stiff. Rinse out juice and salt in cool water, check your results. For severely stained old cotton or linen garments, you may need to repeat this process several days in a row. If fabric is fragile, rinse thoroughly under cool running water, line dry and then iron.
Stains containing iron, rust, and some fruit- and vegetable-juices can actually be made worse by bleach.
Some fabrics with high-synthetic content do not respond very well to any whitening methods because, with age and exposure to light, they undergo a chemical process called "optical darkening." Sheer curtains are a frequent example of this, and you may just have to bin them. Antique and old fabrics are best gently washed by hand with as little complex chemical-whitening as possible. Fibres are already fragile and will be further stressed by heavy-handed treatment.