Hi op, I don’t have melasma but I have hyperpigmentation under my eyes and am pregnant, so I’ve been researching melasma a lot lately.
They key thing is sun avoidance. I wear a wide-brimmed hat and sunglasses when it’s sunny. I also became a lot more diligent about sunscreen use - I’ve been using sunscreen on my face/neck daily since I was in my teens but clearly didn’t do it properly for many years! You need to apply the right amount so that it forms a “film” over your skin, and not disrupt the film by rubbing anything on top. This means that any cream makeup eg blusher is out. With regards to how much to apply, we ned to see sunscreen as a medication (which it is), so if the dose is less then the recommended one it will not work as well. Most sources recommend 1/4 teaspoon for face, plus the same amount for the neck. This is way too much for me (I have a small face, low-ish forehead and hair that covers the back of my neck) so I use enough to “see” the sunscreen coating my skin and then leave it to absorb for a bit.
In the past month or so I also started using sunscreen at home during the day, because I work facing a window.
Many sunscreens are not wearable once you wear the proper amount, so it may take some trial and error to find one that you like. I am really liking NiveaUV face sensitive. They also have a shine control version that is supposed to be even better at leaving no shine or white cast.
With regards to treatments, tranexamic acid products have good evidence of effectiveness. I’m using the Inkey list tranexamic acid serum at night, only started 2 weeks ago so can’t judge the effects yet. Other lightening agents that may work are arbutin, glycolic or lactic acid and licorice extract. Skinceuticals have a serum with tranexamic acid and arbutin, I can’t use it at the moment as arbutin isn’t recommended in pregnancy, but it looks good - it’s often recommended to combine agents when treating hyperpigmentation.
If your melasma is really bothering you it’s worth seeing a dermatologist. They can prescribe tretinoin and other agents (I can’t remember if hydroquinone can be prescribed in the UK or not-I think it was banned by the EU?). Skin + me or Dermatica may be a good way to try these agents without shelling out for a private dermatology consultation.