@steonia It depends on what’s causing your dark circles.
Sun damage: Look for products containing retinol, kojic acid, vitamin C, niacinamide, or arbutin—and make sure they’re safe to use under your eyes. When in doubt, ask a dermatologist.
Some of my undereye darkness was caused by sun damage, and Dr. Dennis Gross Skincare Ferulic + Retinol Triple Correction Eye Serum knocked it out within 3 months. Your mileage may vary, of course, and there might be another product that’d work better for you. I use an OTC retinol serum (usually The INKEY List Retinol Fine Lines and Wrinkles Serum 1 oz/ 30 mL , but I recently began testing SOBEL SKIN Rx 4.5% Retinol Night Treatment ) on my whole face every other night, and I apply it under my eyes—but I don't bring it all the way up to my lower lash line.
Allergies (sinus pressure, inflammation, and/or frequent eye rubbing): Good ol’ antihistamines can help, which you’d likely be taking anyway for other allergy symptoms.
Each spring and summer is Claritin-D time for me, and I try not to rub my eyes much to avoid causing more undereye darkness.
Cold compresses also help me a lot here: something as simple as a cool wet washcloth over my eyes. Also great are refrigerated eye patches that contain anti-inflammatory ingredients like green tea, licorice root, and centella asiatica. There are other soothing ingredients, like chamomile, that work great for other people's inflammation but not so much for mine; eh, might work for you. My favorite eye patches are JayJun Green Tea Eye Gel Patches, and I keep them in the fridge. But I'm sure there are other great patches out there.
Lack of sleep: Products containing caffeine can possibly help. You can also try plumping the skin a bit with products containing hydrating/moisturizing ingredients like hyaluronic acid, glycerin, ceramides, squalane, etc.
You don’t need to use a product specifically marketed as “eye cream." A full face moisturizer or a facial oil can work fine under your eyes. Just make sure your undereye skin isn't completely dried off before you apply the moisturizer: try applying it to somewhat damp skin.
Sunken skin (hollow tear troughs): Plumping up the sunken skin can reduce this darkness. Injectable fillers like Restylane or Juvaderm provide the best and fastest results, though they’re temporary.
You can also try a topical hydrating/moisturizing product to plump the skin, but it won’t give you anywhere near an injectable’s results.
I still have this kind of undereye darkness. I’m not willing to go the injectables route yet, so I rely on hydration/moisturization and concealer/color corrector in my tear troughs. I usually apply BECCA Cosmetics Ultimate Coverage Longwear Concealer Cinnamon under my eyes (and I don't slather it on the way "beauty influencers" do; I use a very tiny amount, literally 2-3 dots under each eye). Then I'll sometimes add an even tinier bit of a second lighter concealer, like PAT McGRATH LABS Sublime Perfection Concealer MD24 , only in the deepest part of the hollow trough. This optical illusion brightens the shadow in that area, making it appear lifted.
Sometimes I'll instead use a bit of highlighter in my tear trough, just to bounce some light off those shadows.
Your genes (hereditary dark circles):You could try products that target hyperpigmentation but honestly, color correction products and/or concealers are your best bet.