Laundry starts to smell bad because the dirt and moisture is a breeding ground for odour-causing bacteria and mildew. In extreme cases, even after a regular wash, some pieces of laundry will still have an odour. There are a few simple things you can do to deodorise your laundry using items that you probably already have around the house.
Sprinkle baking soda in your laundry when it is sitting in the hamper waiting to be washed. Pour a cup of baking soda into the wash, along with your regular detergent. Baking soda is very effective at neutralising and removing odour from your fabrics.
Use a scented fabric softener that has a deodorising agent (for example, Bounce with Febreze). Pour a capful in every wash---a cap and a half when the load has a very strong smell.
Wash your laundry in white distilled vinegar and water. Vinegar is a natural deodoriser. Fill your washing machine with plain hot water and then add a cup of vinegar. After that wash is completed, wash the load once more with regular detergent. This option should be reserved for very odorous laundry.
Place dryer sheets in your laundry; you can add two or three of them to your hamper and to both your wash and dry cycles to help get rid of odour.
Use borax (sodium tetraborate decahydrate), another household product, in your laundry to deodorise your clothes. Add a half a cup to your load. Borax also helps boost the power of your detergent.
Allow your clothes, towels, and fabrics to air-dry before you put them in the hamper. If the moist clothes sit in the hamper for too long, smelly mildew (mould) may form. Separate your very smelly laundry from the ones that are just a little dirty. Keep two hampers---one for the dirty items (for instance, ones that simply have stains) and ones that stink (like workout clothes). If any of your clothes really stink, you may want to toss them in the trash rather than wash them with the rest of your load. The smell could transfer to the other items in your laundry.