Tranexamic Acid - put it into google search and lots of products will appear across the top with links to the different brands and reviews - the percentage of the ingredient in each product will make a difference to the price. I use FaceTheory Exaglow serum which has tranexamic acid as one of the ingredients but there are cheaper alternatives available. Lots under £10 so worth a try but wear factor 30/50 every day of the year, even in winter, it is light that causes the damage, it doesn't have to be sunny. Lots of moisturisers now have sun factor added to the mix, which is the easiest way to wear SPF every day.