Fraying in a sweater occurs when thread starts to unravel because the sweater is snagged, a hole is formed or the thread loosens along edges. Fraying can make a sweater look worn and dated. In order to fix fraying within a sweater, you have to fix either the hole or snag or the edge that started the fraying. Otherwise, the fraying will continue to worsen. If your sweater has a very tiny snag that is barely noticeable, your best bet is to conceal the fraying and then prevent the thread from unraveling further. If your sweater is fraying around the edges, you'll need to mend it on the sewing machine.
Fixing Fraying Around Small Snags or Holes
Use a sewing needle to carefully push the unraveled, frayed thread from the outside of the sweater to the inside. This will hide the fraying.
Turn the sweater inside out and use the hook on a crochet hook to pull the frayed thread tight.
Knot the frayed thread on the inside of the sweater.
Coat the knot with a thin layer of clear nail polish to prevent further fraying.
Fixing Fraying Around Edges
Coat the frayed edges on your sweater such as sleeves or the bottom circumference of the sweater with clear nail polish. Let the polish dry.
Turn the sweater inside out.
Turn the edging up twice so that all the fraying is covered and pin in place with straight pins.
Place the sweater on the sewing machine and create a new seam by sewing around the edges using a thread that matches the sweater so it blends in.