Why retinoids matter

Topical vitamin A is one of the most widely studied ingredient categories in dermatology. A 2006 review in Clinical Interventions in Aging concluded that retinoids reduce the visible signs of photoaging by stimulating collagen synthesis, normalising desquamation and increasing epidermal turnover.^[1] A landmark 2007 trial published in Archives of Dermatology showed that 0.4% retinol applied three times weekly for 24 weeks visibly improved fine lines and roughness in older adults compared with vehicle.^[2]

Skin only "uses" one form: retinoic acid

All cosmetic vitamin A actives must convert to retinoic acid — the molecule the retinoid receptor recognises — before any biological effect occurs. The conversion pathway is well-characterised:

• Retinyl esters → retinol → retinaldehyde → retinoic acid (3 steps)
• Retinol → retinaldehyde → retinoic acid (2 steps)
• Retinaldehyde → retinoic acid (1 step)

This is why the same applied dose of different vitamin A forms produces different rates of activity in the skin. A 2021 systematic review in The Journal of Clinical and Aesthetic Dermatology concluded that over-the-counter retinaldehyde formulations show measurable improvements in facial photoageing markers in clinical studies, sitting between retinol and prescription tretinoin in onset of effect.^[3]

Crystal Retinal® at a glance

Medik8® Crystal Retinal® uses encapsulated retinaldehyde stabilised in a vehicle that releases the active gradually overnight. The range steps in concentration so users can build tolerance:

• Crystal Retinal 1 — entry strength, suited to sensitive or first-time users
• Crystal Retinal 3 — early build-up
• Crystal Retinal 6 — daily use once tolerated
• Crystal Retinal 10 — advanced
• Crystal Retinal 20 — high tolerance only

What clinical research shows

Independent clinical work has examined retinaldehyde directly. A 2018 randomised controlled study compared a retinaldehyde-based cream against a series of glycolic acid peels and found the topical retinaldehyde regimen produced comparable improvements in clinical signs of facial ageing.^[4] A 2021 split-face study published in Journal of Cosmetic Dermatology reported that a multilamellar-vesicle formulation containing retinaldehyde was well tolerated and improved skin parameters over 12 weeks.^[5]

How to introduce vitamin A safely

• Start low, build slowly. One night a week for the first two weeks; alternate nights from week three; nightly only when no irritation persists.
• Apply to dry skin in the evening. Damp skin can increase absorption and irritation.
• Always use SPF in the morning. Vitamin A increases sun sensitivity. A broad-spectrum sunscreen is non-negotiable while using retinoids.
• Avoid mixing with strong acids the same night. Layering with high-strength AHAs/BHAs can compound irritation.
• Pregnancy and breastfeeding. Topical retinoids are generally not recommended during pregnancy or breastfeeding. Speak with your doctor or midwife.

About those "times faster" numbers

You will have seen retinal called eleven times faster than retinol, or twenty times stronger, or some other tidy figure. We are not going to print one. No published head-to-head trial in human skin has measured a speed ratio between the two, and none of the studies below attempted it. Those numbers come from marketing copy, not from a paper.

Tolerance, and a claim worth correcting

Retinal is often sold as the gentler choice compared with retinol. The direct evidence for that is thin.

Fluhr et al., 1999 is the study usually pointed at. It compared retinol, retinaldehyde and retinoic acid in repeated patch tests, and that part of the study had six people in it. Six. Retinol and retinaldehyde came out with an equally low irritation potential. Retinoic acid was clearly the most irritating of the three.

Even at that size the picture is mixed. Retinaldehyde and retinoic acid caused more scaling than retinol. Retinol and retinoic acid tended to cause more burning and itching than retinaldehyde, though that difference was not statistically significant.

The much larger part of that study, 355 people over 44 weeks, compared retinaldehyde with retinoic acid only. Retinol was not in it.

So retinal's comfort advantage is over prescription retinoic acid. Over retinol, nobody has really shown it. If a retinol already suits you, such as Intelligent Retinol 6TR, there is nothing in this evidence telling you to switch shelves.

The Crystal Retinal ladder, read honestly

The number on the bottle is the percentage. 1 is 0.01%, 3 is 0.03%, 6 is 0.06%, 10 is 0.1%, 20 is 0.2%.

The published retinaldehyde trials sit at 0.05% and 0.1%. That puts Crystal Retinal 6 and Crystal Retinal 10 closest to the concentrations that have actually been studied.

The 20 sits past the evidence. No study cited here tested 0.2%. Saurat's group tested 0.5% and 1%, where tolerance fell away, and nothing in between has been published that we can point you to. We stock it, and we would rather say that plainly than imply trial backing that does not exist, which is why we have not linked it here.

Higher is not automatically better either. Kwon's group found the same texture and hydration results from 0.1% and 0.05%. Deda's group found more change in the wrinkle measurements from 0.1%, over 24 weeks. Both of those are as much about time as about strength.

We would rather you stayed on a comfortable rung for a year than gave up on a strong one by March.

What retinal and retinol cannot do

This part matters more than the ladder.

• These are cosmetic products, not medicines. They do not treat, cure, prevent or heal acne, rosacea, melasma, sun damage or ageing. Everything above is about the appearance of skin.
• They do not replace a prescription retinoid. Siddiqui et al., 2024 reviewed 25 studies comparing tretinoin with other topical products and concluded that most of them are poor quality or show bias, and that there is not enough evidence to name an alternative first-line option. Retinaldehyde is listed there among the agents that can be considered second-line for people who cannot tolerate tretinoin.
• They are not a fix for pigmentation. In Kwon's study one instrument reading of melanin moved by 6.5%, and only in the 0.1% group, which was around twenty people. That is not a reason to use retinal on dark marks or melasma.
• The evidence base is narrow. Forty women in one study, fifty-six in another, one hundred and twenty-five in the largest. Creidi 1998 and Fluhr 1999 share three of their authors. None of these papers names the product it tested, the three oldest predate Crystal Retinal by about two decades, and none was run in a New Zealand population.
• Conversion depends on your own enzymes, and those are not fully mapped. The tracer work points to most of what you apply going into storage rather than straight to the active form.
• Pregnant or breastfeeding? The evidence on topical vitamin A derivatives is not settled. Stop, and talk to your doctor or midwife. We are not going to reassure you here.
• Layering rules are guesswork. No trial we can find has tested whether using retinal alongside exfoliating acids or vitamin C on the same night helps or harms. Keep it simple while you settle in, but treat that as caution rather than a finding.

Bottom line

Retinaldehyde is one chemical step closer to retinoic acid than retinol is, which the literature suggests can translate into faster visible response when formulated and stabilised properly. Medik8® Crystal Retinal® is one of the best-known retinaldehyde ranges and is widely available in NZ through authorised stockists like Verdo.