Retinoids- What they are and how they work?

Few skincare ingredients are as well studied — or as widely misunderstood — as retinoids. They are the closest thing skincare has to an all-rounder: the same vitamin A derivatives that smooth fine lines also support clearer, more even skin. But the word "retinoid" covers a whole family of molecules with very different strengths, and most of the frustration people have with them comes from picking the wrong one, or starting too fast.

This guide explains what retinoids actually are, how they work in the skin, how the main forms differ in strength, and how to introduce one without the redness and peeling that make so many people give up in the first month.

What are retinoids?

"Retinoid" is a collective name for vitamin A (retinol) and its natural and synthetic derivatives [1]. They share a common ability: once in the skin they influence how skin cells behave — how quickly they renew, how much collagen the deeper layers produce, and how evenly pigment is distributed. That is why a single ingredient family is associated with so many different benefits, from smoother texture to a more even tone.

The forms you will see on an ingredient list differ in potency, and that difference is the single most useful thing to understand before you buy. The main cosmetic forms, from gentlest to strongest, are retinyl esters (such as retinyl palmitate), retinol, and retinaldehyde (also called retinal). The prescription form, retinoic acid (tretinoin), is the active molecule the others ultimately become.

How retinoids work in the skin

Whatever form you apply, the skin has to convert it into retinoic acid — the only form that is biologically active. Retinoic acid binds to retinoic acid receptors inside skin cells and switches on a cascade of effects: it stimulates the growth of keratinocytes and fibroblasts and prompts fibroblasts to produce more extracellular matrix, including collagen [2]. Topical retinoids are recognised for promoting collagen synthesis and for inhibiting matrix metalloproteinases — the enzymes that break collagen down [1].

That combination matters for ageing skin in particular. Loss of firmness over time is driven partly by collagen breakdown; an ingredient that both encourages new collagen and slows its degradation works on the problem from two directions at once. This is why retinoids feature so consistently in evidence-based anti-ageing care.

The retinoid family, from gentle to strong

The reason the forms differ in strength comes down to conversion. Each form has to be metabolised through a chain of steps to reach retinoic acid, and every extra step costs potency.

• Retinyl esters → retinol → retinaldehyde → retinoic acid (three steps). The gentlest and least potent.
• Retinol → retinaldehyde → retinoic acid (two steps). The most common over-the-counter form.
• Retinaldehyde (retinal) → retinoic acid (one step). More potent than retinol, yet still cosmetic.
• Retinoic acid (tretinoin) — already active, prescription only.

Because retinaldehyde is only a single conversion away from retinoic acid, it is more potent than retinol, while the prescription acid — being already active — tends to cause more irritation than the converted forms [1]. The practical takeaway: stronger is not automatically better. The best form is the most potent one your skin can use comfortably.

For a deeper look at retinaldehyde specifically — and who it suits — see our dedicated article on retinal.

Why retinaldehyde is a useful middle ground

Retinaldehyde is worth singling out because it resolves the usual trade-off between strength and tolerability. In the skin it is metabolised to retinoic acid in a single step, so it delivers genuine retinoid activity. Yet in clinical work it has been notably well tolerated: in a study of topical retinaldehyde, the 0.05% and 0.1% preparations applied to facial skin were well tolerated and allowed prolonged use — up to three years — in patients with inflammatory skin conditions, while still producing a dose-dependent increase in epidermal thickness [3].

That is the appeal of a well-formulated retinaldehyde: meaningful results with a lower likelihood of the stinging and flaking that lead people to abandon stronger retinoids.

What retinoids can — and cannot — do

Realistic expectations are part of using retinoids well. With consistent use over months, retinoids are associated with smoother texture, softening of fine lines, more even tone and support for clearer, blemish-prone skin.

What they are not is an overnight fix. The skin changes they drive — renewed cells, new collagen — take time to accumulate, and the first few weeks can actually look worse before they look better as skin adjusts. Patience and consistency matter more than strength. It is also worth knowing that retinoids and vitamin C are both useful but ask different things of a routine; how to combine them is a topic in its own right.

How to start without irritating your skin

The single biggest reason people fail with retinoids is starting too strong, too often. The adjustment period — sometimes called retinisation — is when skin gets used to the ingredient, and it is much smoother if you ease in.

A sensible approach: choose a cosmetic strength appropriate to your experience, apply it only in the evening, start two to three times a week, and increase frequency only once your skin stays comfortable. Use a small amount — a pea-sized portion is enough for the whole face — and if redness, irritation or dryness appears, pause for a few days until it settles, then resume. Buffering with a moisturiser and keeping the rest of the routine simple both help.

Two rules are non-negotiable. First, retinoids are evening ingredients. Second, daily sunscreen is essential while using them — both to protect the freshly renewed skin and to preserve the results you are working for.

The Ph.Doctor approach to retinoids

Ph.Doctor is a dermocosmetics line developed by Dr. Nina Wiśniewska and biotechnologist Anna Sienkiewicz, built on a "less is more" philosophy: few ingredients, each with a defined function. Its retinoid range is built around a stable form of retinaldehyde, encapsulated to release gradually — the middle-ground form described above — in two strengths for different needs and experience levels.

For the face, the RetinALL IN ONE Face cream 0.1% is the stronger option.

RetinALL IN ONE Face cream 0.1% is, per its product card, a cream "with a stable form of retinal 0.1%… encapsulated in cyclodextrin γ," a technology that "provides stability for 12 months after opening." It is described as a "balanced formula with minimal risk of irritation, thanks to the slow release system," is "anti-wrinkle, reduces hyperpigmentation, against imperfections, suitable for sensitive skin," and notes that "the action of retinal improves the appearance of acne-prone skin." Application follows the cautious pattern above: "apply a pea-sized portion… gently spread over the entire face (initially 2–3 times a week at night)," followed in the morning by "SPF 50 sunscreen"; if irritation appears, "take a break for a few days until symptoms subside," then build back up "until you develop full tolerance."

For those who also want to treat the body — or prefer a lower strength — the FACE & BODY RetinALL 0.05% is the gentler option.

FACE & BODY RetinALL 0.05% is a face-and-body cream with a stable form of retinal at 0.05%, also encapsulated in cyclodextrin with a slow-release system for "minimal risk of irritation." Per its card it is intended for all skin types, especially those with signs of skin ageing or a tendency to blemishes, is applied in the evening (the face starting 2–3 times a week, building to tolerance) and followed by SPF 50 in the morning. Note the indications: this product is contraindicated for pregnant women, though listed as suitable while breastfeeding per e-lactancia.org. As always, anyone pregnant, breastfeeding or under dermatological care should check with a professional first.

Whichever you choose, the principle is the one running through this article: pick the form your skin can use comfortably, start slow, and protect the result with daily sun protection.

Frequently asked questions

What is the difference between retinol and retinal?

Both are cosmetic vitamin A derivatives, but they differ in how close they are to the active form. Retinol needs two conversion steps to become retinoic acid, while retinaldehyde (retinal) needs only one. That makes retinal more potent than retinol at comparable concentrations, although it can also be felt sooner by reactive skin. Many people find a well-formulated retinal a good balance of results and comfort.

When should I apply a retinoid?

In the evening. Retinoids are used at night as part of your PM routine, on clean, dry skin. Daytime use is not recommended; instead, the focus during the day is sun protection. Applying at night and following with SPF in the morning is the standard, and it is exactly what Ph.Doctor's RetinALL instructions describe.

Do I need to use SPF with a retinoid?

Yes — daily, and it is not optional. Sunscreen protects the freshly renewed skin a retinoid produces and preserves the improvements you are working towards. A broad-spectrum SPF of at least 30 (the RetinALL cards specify SPF 50) used every morning is part of any retinoid routine, not an add-on.

Why is my skin peeling and red after starting a retinoid?

This is the adjustment period, sometimes called retinisation, and it is common in the first weeks. It usually means you are using too much, too often. Reduce frequency to two or three evenings a week, use only a pea-sized amount, buffer with a moisturiser, and pause for a few days if irritation flares — then resume and build up slowly. The reaction typically settles as the skin adapts.

Can I use a retinoid if I have sensitive skin?

Often yes, with the right form and pace. Gentler, well-tolerated forms such as a low-strength encapsulated retinaldehyde are designed to reduce irritation, and starting slowly makes a big difference. Patch-test first, begin once or twice a week, and keep the rest of your routine simple. If your skin is highly reactive or you have a skin condition, check with a professional before starting.

How long until I see results from a retinoid?

Plan in months, not days. The cell renewal and collagen support that retinoids drive take time to accumulate, and most people need consistent use over several weeks before changes in texture and tone become visible. The first few weeks can even look worse as skin adjusts. Consistency matters far more than chasing a stronger product.

Can I use a retinoid with vitamin C or acids?

You can, but not carelessly. Retinoids, vitamin C and exfoliating acids are all active ingredients, and stacking them in the same routine raises the risk of irritation, especially while you are still building tolerance. A common approach is to separate them — for example acids or vitamin C in the morning and a retinoid at night — and to introduce only one new active at a time.

Are retinoids safe during pregnancy?

Topical retinoid use in pregnancy is generally approached with caution, and individual products carry their own guidance. Ph.Doctor's FACE & BODY RetinALL 0.05%, for instance, is contraindicated for pregnant women per its product card. If you are pregnant or planning to be, do not start a retinoid without first checking with your doctor.

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Selected references

1. Mukherjee S, Date A, Patravale V, Korting HC, Roeder A, Weindl G. Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety. Clin Interv Aging. 2006;1(4):327–348. Reviews the retinoid family, receptor mechanism, collagen stimulation and MMP inhibition, and the metabolic conversion of the different forms to retinoic acid.
2. Fisher GJ, Voorhees JJ. Molecular mechanisms of intrinsic skin aging and retinoid-induced repair and reversal. J Investig Dermatol Symp Proc. 1998;3(1):57–60. Retinoic acid stimulates growth of keratinocytes and fibroblasts and stimulates extracellular matrix (collagen) production by fibroblasts.
3. Saurat JH, Didierjean L, Masgrau E, et al. Topical retinaldehyde on human skin: biologic effects and tolerance. J Invest Dermatol. 1994;103(6):770–774. Retinaldehyde produced a dose-dependent increase in epidermal thickness; 0.05% and 0.1% facial preparations were well tolerated and allowed prolonged use (up to 3 years).