Most DIY serum articles are lying to you, and the lie is specific. Mashing fruit into yoghurt does not make a serum. A serum is a thin, high-concentration delivery system for one or two actives, and the reason the good ones cost money is formulation work, pH control, and preservation. You cannot beat a prescription retinoid with a blender.
What you can beat is the markup. There are exactly two categories where a home version genuinely matches or outperforms the shelf: oil-based serums, where there is no water and therefore no formulation problem at all, and single-active water serums made from raw powders, where you are buying the same molecule the brand buys and skipping their packaging. A 100ml batch of the recipes below costs roughly what 10ml of the retail equivalent does.
Read the preservation section before you make anything with water in it. That part is not optional.
1. Barrier repair oil serum
Twenty millilitres squalane, five millilitres cold-pressed rosehip seed oil, four drops tocopherol (vitamin E).
Pour into a 30ml dropper bottle, cap, invert a few times. That is the whole method. Two to three drops onto damp skin at night, pressed in rather than rubbed.
This is the recipe where DIY wins outright, and it is not close. Squalane is the base of a genuinely large number of expensive facial oils. It is a single molecule, it does not oxidise, and it sits at almost the same molecular size as the sebum your skin already makes, so it absorbs without that slick film. Rosehip brings linoleic acid, which matters if your skin is oily and dehydrated at the same time, because low linoleic acid in sebum is associated with clogged pores. The vitamin E is there to keep the rosehip from going rancid, not for your face.
One honest correction while we are here. Rosehip oil is marketed as a natural retinoid. It contains trace all-trans retinoic acid at levels far too low to do what a retinoid does. Buy it for the fatty acids and stop expecting it to resurface anything.
No preservative needed. There is no water, so nothing can grow. It keeps six to nine months in a dark bottle.
2. Niacinamide serum from powder
Four grams niacinamide powder, 95ml distilled water, 1ml glycerin, preservative at the rate on its label.
Warm the distilled water slightly, stir the niacinamide in until the liquid runs clear with no grit at the bottom, add glycerin, then the preservative last once it has cooled. Check pH with strips. You want somewhere between 5 and 6. Bottle it.
Four to five percent is the concentration that shows up in most of the research on sebum regulation and pigmentation, and it is where I would stop. The 10 percent versions on the market are not twice as good, they are just twice as likely to leave you flushed and stinging, and a slice of people react to niacinamide at that level regardless. Starting low and going up is free when you are mixing it yourself.
Give this eight to twelve weeks. Niacinamide is slow and unglamorous and it works.
3. Hyaluronic acid hydrating serum
One gram HA powder, ideally a low and high molecular weight blend, into 100ml distilled water, plus 3ml glycerin and preservative.
Sprinkle the powder across the surface of the water rather than dumping it in, or you get a lump with a dry centre that never dissolves. Leave it alone for two hours. Do not stir it aggressively. It will hydrate into a clear gel on its own, and stirring early just makes clumps you will be picking at all evening.
The important part is how you use it, and this is where most people get worse results than the bottle promised. Hyaluronic acid holds water, it does not create it. Apply to damp skin and put something occlusive over the top within a minute, a moisturiser or the oil serum from recipe one. In dry air, on dry skin, with nothing sealing it, HA can pull moisture out of the deeper layers instead of into them and leave you tighter than when you started. If your serum has ever made your face feel crunchy, that is why.
4. Vitamin C serum, the version that actually survives
Three grams sodium ascorbyl phosphate, 96ml distilled water, 1ml glycerin, preservative.
Dissolve the SAP in the water, add glycerin and preservative, check that pH lands around 6 to 7. Amber or opaque bottle, and keep it out of the bathroom window.
Now the part you need to hear. Do not make L-ascorbic acid serums at home. Pure vitamin C needs a pH near 3.5 to penetrate, oxidises on contact with air and light, and the well-known formulations that hold it stable took real work with ferulic acid and tocopherol and airless packaging. A kitchen batch will be brown and useless inside a week, and brown vitamin C is not just weak, the oxidation products can irritate. That is genuinely one of the few places where paying for a good commercial formula makes sense.
Sodium ascorbyl phosphate is the workaround. It is a stable derivative, it holds up at skin-neutral pH, and it converts to ascorbic acid on the skin. Slower and gentler than the 15 percent stuff. Also the only vitamin C worth mixing yourself.
Preservation, which is the whole ballgame
Anything containing water grows bacteria, yeast and mould. Distilled water, boiled water, filtered water, all of it. Within days, sometimes without changing colour or smell, and you are putting it on your face near your eyes.
The fridge does not preserve anything. It slows growth. A refrigerated unpreserved serum is a contaminated serum on a delay.
Use a broad spectrum preservative and use it at the rate the supplier lists, not less. Liquid Germall Plus sits around 0.5 percent. Geogard ECT is closer to 1 percent. Optiphen Plus lands somewhere between. Add it after the mix has cooled, because heat degrades some of them. Vitamin E is not a preservative, it is an antioxidant for oils. Grapefruit seed extract is not a preservative either, whatever the label says.
Sanitise your bottles and stirrers with 70 percent isopropyl alcohol and let them air dry. Make small batches. Two months is a sensible life for a home serum even with preservative, and if anything separates, clouds, smells off or grows a speck of anything, bin the whole thing without negotiating with yourself.