PRIORI TETRA's 4 Levels and the fx Code, Decoded

TETRA is not a technology that runs through the whole PRIORI range. It is the name of one specific line, PRIORI's sun protection, and the "four levels" are four categories of environmental exposure the formula is built to screen: UVA and UVB, high-energy visible (HEV) blue light, infrared heat, and free-radical activity from pollution and general oxidative stress. That is all it means. If you have seen TETRA described online as a four-part acronym standing for turmeric, environmental defence, total antioxidants and so on, someone made that up. It does not come from PRIORI.

Once you know that, the rest of the range reads much more easily, because PRIORI names everything the same way, and the naming carries more information than most brands' does. This guide decodes it: what the four TETRA levels actually cover, what evidence sits behind each one, and how the LCA, Q+SOD, DNA and TETRA prefixes and fx numbers tell you exactly what a product is before you read a word of the description.

The four levels, one at a time

PRIORI packages these under a trademark it calls Genetic Protection Factor (GPF). Ignore the branding for a moment and look at what is actually being screened, because the four levels are not equally well supported by evidence, and it pays to know which is which.

1. UVA and UVB, the well-established one

TETRA uses zinc oxide and titanium dioxide as its filters, which makes it a mineral (physical) sunscreen rather than an organic-filter one. Broad-spectrum SPF helping to prevent UV damage is the single best-evidenced thing in all of skincare, and this level is doing the heavy lifting. Everything else in the formula is an addition to it, not a substitute for it.

One labelling note if you are comparing UK and US listings: UK and EU sunscreen labelling stops at "50+", so a formula testing above 50 gets labelled 50 or 50+ no matter how far above it tests. US labelling has no such ceiling. A UK SPF 50 is therefore not automatically weaker than a US listing showing a bigger number, though you cannot confirm from the number alone that they are the same formula either.

2. HEV blue light, plausible, still developing

Visible light in the blue-violet range is the level that draws the most marketing attention and has the least settled evidence. What is reasonably established is that visible light can trigger a pigment response in the skin, and that this matters more for deeper skin tones, where the response tends to hang around longer than the one UVA alone produces. Where the evidence gets much thinner is the everyday claim that screen exposure is a meaningful contributor. The light coming off a phone or laptop is orders of magnitude weaker than daylight, and daylight is where almost all your HEV exposure comes from.

In practice, screening visible light in a sunscreen is done with pigment. That is why tinted mineral formulas are the usual recommendation for anyone whose main worry is pigmentation rather than burning. It is also the practical reason to check which TETRA you are buying: the tinted version carries a mineral colour guide that blends out on application, and the untinted one does not. If uneven tone is your primary concern, our guide to products for hyperpigmentation covers where a tinted SPF sits alongside the rest of a routine.

3. Infrared heat, the least discussed

Infrared is heat radiation, and it accounts for a large share of the energy reaching your skin from the sun. PRIORI addresses this level with melanin and an ingredient marketed as Soliberine. Infrared is a real exposure route rather than a marketing invention, but no cosmetic ingredient blocks it the way a UV filter blocks UV. The approach is to load the formula with antioxidants that mop up the free radicals heat exposure generates. Treat this level as a sensible extra rather than a shield.

4. Antioxidant defence

The fourth level is carnosine plus the formula's broader antioxidant content, aimed at free radicals from pollution and oxidative stress. This is standard practice in premium sunscreens now and the least distinctive of the four. It is also the level most easily covered by other products, which matters when you are deciding whether TETRA earns its place or whether a vitamin C step in the morning already does the job.

How to read a PRIORI product name in five seconds

Here is the genuinely useful part, and almost nothing online explains it. Every PRIORI product carries a line prefix and an fx number, and both mean something.

The prefix tells you which complex is inside

• LCA, built around PRIORI's LCA Complex: pH-correct lactic acid with vitamins A, C and E. This is the gentle, everyday, barrier-friendly end of the range. Concentrations swing sharply by product: the fx110 cleanser carries 13% LCA Complex, the fx140 moisturiser only 2%, because one is rinsed off and one stays on.
• Q+SOD, CoQ10 (ubiquinone) plus superoxide dismutase, an antioxidant enzyme. This is the more active tier: the fx220 Brightening Serum layers 15% lactic acid and 0.15% retinol on top of the antioxidant base, with liquorice root and mulberry leaf as botanical brighteners.
• DNA, built on what PRIORI calls its DNA Enzyme Complex, a group of enzyme-derived ingredients sourced from microbe, algae and mustard seed extracts. This is the most expensive tier and the one where you should read claims most carefully; the category is interesting, but the independent evidence base for these ingredients in leave-on cosmetics is far smaller than for retinoids, vitamin C or sunscreen.
• TETRA, sun protection, as covered above. One job, in two variants: an untinted lotion and a tinted one.

The fx number tells you the product category

Look at the middle digit. Across the whole range it holds:

• x1x, cleanser (LCA fx110, Q+SOD fx210)
• x2x, serum or leave-on treatment (LCA fx120, Q+SOD fx220, DNA fx221)
• x3x, eye product (LCA fx130, DNA fx231)
• x4x, moisturiser (LCA fx140, Q+SOD fx240, DNA fx241)
• x5x, sun protection (TETRA fx250 untinted, TETRA fx251 tinted)
• x6x, exfoliant or mask (LCA fx160, LCA fx161, Q+SOD fx261)

The first digit tracks the generation: 1 for the original LCA line, 2 for the Q+SOD, DNA and TETRA lines. The last digit sorts variants within a category, so fx140 is the facial moisturiser and fx141 the hand and body version. Same again in sun protection, where fx250 and fx251 are the untinted and tinted lotions.

So "LCA fx141" decodes to: original lactic acid line, moisturiser category, second variant. You know it is a body cream before you read anything.

One caveat, and it lands on that last digit. Retailer listings, ours included, do not always carry the code the carton does, and TETRA is where this goes wrong most often: fx250 and fx251 get used interchangeably in titles even though only one of them is tinted. If the tint is what you are deciding on, go by the packaging and the ingredient list rather than the listing title. That is exactly the situation the decoder is good for.

Which line actually suits you?

Start with LCA if your skin is reactive, easily overloaded, or new to acids. The fx110 cleanser and fx140 Barrier Restore Complexe are the two most forgiving products in the range. The fx140 pairs ceramides, cholesterol and fatty acids with a low acid load, which is the right structural approach when your skin barrier is under strain. If you are not sure lactic acid is even the right acid for you, our comparison of AHAs and BHAs is the better place to start.

Move to Q+SOD if tone and dullness are your priority and your skin already tolerates actives. The fx220 does three things at once, resurfacing, brightening and retinol renewal, which makes it efficient but also the product most likely to cause trouble if you introduce it too fast or stack it on top of an existing retinoid. Read our retinol guide before you add it to a routine that already has one.

Consider DNA only once the basics are genuinely in place. There is no version of a skincare routine where an enzyme complex outranks daily SPF and a tolerated retinoid. If you are choosing between the DNA fx221 serum and simply wearing sunscreen every day, wear the sunscreen.

TETRA is the exception to that ordering, because it is the sunscreen. If you buy one PRIORI product, this is the defensible one.

Where does TETRA fit, and what does it replace?

TETRA is a morning product and it replaces your existing sunscreen, not your moisturiser and not your antioxidant serum, though it overlaps with the latter. A workable PRIORI morning sequence runs: cleanser (fx110 or fx210), treatment serum, moisturiser, then TETRA last. Nothing goes over the top of it. Our ingredient layering guide covers the order logic in more detail, including what happens when you put actives on either side of an SPF step.

Two practical points. First, mineral filters need generous application to reach their labelled protection, and a tinted formula's colour guide helps here precisely because people under-apply; seeing the coverage before it blends is a rough check on how much you have put on. Second, TETRA is one of several routes to broad-spectrum protection with added antioxidant and visible-light coverage. It is not the only one, and it is not always the easiest to get hold of in the UK. Our roundup of broad-spectrum facial sunscreens works through the alternatives, and the full sunscreen range is where to find a tinted mineral option you can buy today, or a chemical-filter one if you dislike the finish minerals leave.

The honest summary

PRIORI's four-level framing is a fair description of what a modern sunscreen tries to do, and the naming system across the range is unusually informative once decoded. But levels one and four are well-trodden ground, level two is plausible with a developing evidence base, and level three is a sensible hedge rather than a shield. The four levels are a way of organising a good sunscreen, not a category of product that other sunscreens cannot reach.

If the fx codes were what brought you here, that decoder is the thing to keep, because it works on any retailer's listings, not just ours. Our PRIORI range is grouped by line and category if you want to see them side by side, though UK availability moves around and individual codes come and go. When something is not listed, the job it does exists elsewhere: the sunscreen, retinol and lactic acid collections cover the same ground across other brands.