レチノールとは？ビタミンAとの違い・種類・濃度・使い方・A反応・注意点を解説

What Is Retinol? Vitamin A, Types, Strength, How to Use, Retinoid Reactions & Precautions

OBARASOTARO

“Is retinol the same as vitamin A?” “What is the difference between retinol, retinal and tretinoin?” “Is a higher percentage always better?” “What is a retinoid reaction?”

Retinol is one of the most widely discussed ingredients in modern skincare.

At the same time, the terminology can be confusing because names such as vitamin A, retinoids, retinal, retinyl esters, retinoic acid and tretinoin are closely related but do not all mean the same thing.

A label such as “retinol 0.1%” or “retinol 1%” also does not tell you everything about a product. It is useful to consider the type of retinoid, formulation stability, packaging, frequency of use and how well the product suits your skin.

This guide explains what retinol is, how it relates to vitamin A, the different types of retinoids, the differences between retinal and tretinoin, how retinoids are converted in the skin, what clinical research has examined, how to interpret concentration claims, what is commonly called a “retinoid reaction”, how to read information about pores and acne, how to use and store retinol products, pregnancy precautions, and how cosmetic and quasi-drug claims are regulated in Japan.

Contents

What is retinol?

Retinol is a form of vitamin A.

Chemically, it is the alcohol form of vitamin A. Retinol and a wider group of related natural and synthetic compounds are collectively known as retinoids.

Retinol also occurs naturally in the human body and plays a role in vitamin A metabolism.

In skincare, retinol is one of the best-known retinoids used in cosmetic formulations.

A simple way to think about it is that retinol belongs to the larger retinoid family.

Retinol vs vitamin A

Retinol is often described simply as “vitamin A”, but more precisely, retinol is one of several compounds associated with vitamin A activity.

Vitamin A-related compounds include:

  • retinol
  • retinal, also called retinaldehyde
  • retinoic acid
  • retinyl esters

Some carotenoids found in food, including beta-carotene, can also be converted into vitamin A in the body when needed.

Did you know? The name “retinol” is linked to the retina

The “retin-” in retinol is related to the word retina.

Vitamin A plays an important role in vision, which is why many vitamin A-related compounds share names beginning with “retin-”.

Although retinol is now best known as a skincare ingredient, its name reflects its much broader biological connection with vitamin A.

What are retinoids?

Retinoids are a group of compounds that includes vitamin A and related natural and synthetic derivatives.

Some are used in cosmetics, while others are used as medicines in dermatology.

Type Examples General characteristics
Retinyl esters Retinyl palmitate, retinyl acetate Vitamin A derivatives that can be converted into retinol
Retinol Retinol One of the most widely used cosmetic retinoids
Retinal Retinal / retinaldehyde An intermediate between retinol and retinoic acid
Retinoic acid Tretinoin, or all-trans retinoic acid An active form that interacts directly with retinoid receptors

Although their names are similar, these compounds can differ in how many metabolic conversion steps are required, stability, potential for irritation and regulatory status.

How retinyl esters, retinol, retinal and retinoic acid are related

One useful way to understand retinoids is to look at their metabolic conversion pathway.

A simplified pathway is:

Retinyl esters → Retinol → Retinal → Retinoic acid

Retinol is first converted into retinal and then into retinoic acid.

Retinyl esters are converted into retinol before moving further along this pathway.

What is the difference between retinol and retinal?

Retinol and retinal are both vitamin A-derived retinoids, but they differ in how many conversion steps remain before retinoic acid is formed.

Retinol follows: retinol → retinal → retinoic acid, while retinal follows: retinal → retinoic acid.

In actual skincare products, however, the ingredient name alone does not determine how a formula will perform or feel. Concentration, stabilisation technology, formulation, frequency of use and individual skin compatibility should also be considered.

Did you know? Their similar names reflect their shared pathway

Retinol, retinal and retinoic acid have similar names because they are closely related compounds within the same vitamin A metabolic pathway.

When comparing skincare products, it can therefore be useful to look beyond the word “retinol” and check which retinoid is actually being used.

Retinol vs tretinoin

Another name that often appears when researching retinol is tretinoin.

Tretinoin is all-trans retinoic acid itself and is a different substance from retinol.

Retinol must be converted in the skin through retinal before becoming retinoic acid, while tretinoin is already in the retinoic acid form.

Tretinoin is widely studied and used as a prescription medicine in dermatology in many countries.

When reading online research about “retinoids” or “retinoic acid”, it is therefore important to check whether the study concerns cosmetic retinol or a pharmaceutical retinoid such as tretinoin.

Although they belong to the same broad retinoid family, their ingredient forms, concentrations, intended uses and regulatory classifications differ.

How does retinol work in the skin?

Retinol can be converted in the skin through retinal into retinoic acid.

Retinoic acid interacts with intracellular receptors including retinoic acid receptors, or RARs, which are involved in regulating gene expression and a range of biological processes in the epidermis and dermis.

Research on retinoids has examined their relationship with:

  • epidermal cell differentiation
  • keratinisation processes
  • the extracellular matrix
  • collagen-related metabolism
  • components involved in skin hydration

These findings come from dermatological research on retinoids as a group of compounds.

For individual commercial cosmetics, the appropriate way to interpret a product is to look at the efficacy claims and directions that are supported and permitted for that specific formulation.

What does retinol research examine?

Retinol is one of the more extensively studied ingredients used in cosmetic skincare.

Clinical studies continue to investigate retinol-containing formulations in relation to the appearance and structure of photoaged skin.

For example, a 2024 analysis combined six vehicle-controlled studies using a stabilised 0.1% retinol formulation.

The analysis included 237 women in the retinol group and 234 in the vehicle group, mainly with mild to moderate signs of photoageing, and evaluated outcomes over 12 weeks.

Compared with the vehicle group, the retinol group showed changes across several assessed parameters, including fine-line appearance, skin tone and overall photoageing measures. Most reported irritation-related effects were described as mild to moderate.

However, retinol studies can differ considerably in concentration, formulation, stabilisation technology, treatment period and participant characteristics.

When reading research, it is therefore useful to check which retinoid was used, at what concentration, in what type of formulation and for how long.

How should you read information about retinol, pores and acne?

When researching retinol online, you may often see it discussed together with words such as “pores” and “acne”.

The broader retinoid family includes pharmaceutical ingredients used in dermatology, including medicines used in acne treatment.

These medicines differ from cosmetic retinol products in their ingredient form, concentration, intended purpose and regulatory classification.

It is therefore important to separate research on pharmaceutical retinoids from information about retinol used in ordinary cosmetics.

For cosmetic products, refer to the efficacy claims and directions that are permitted and supported for the individual product.

Understanding the distinction between what has been studied with retinoid medicines and what can legitimately be claimed for a cosmetic retinol product makes online skincare information easier to interpret.

Is a higher retinol concentration always better?

Retinol products may display concentrations such as “0.1%”, “0.3%”, “0.5%” or “1%”.

Different concentrations are also used in clinical research, but in practice it is more useful to consider the overall formulation rather than concentration alone.

Factors that can affect the characteristics and tolerability of a retinol product include:

  • the actual concentration of retinol
  • the type of retinoid
  • encapsulation or other delivery technologies
  • stabilisation methods
  • the presence of moisturising ingredients
  • frequency of use
  • light-protective or air-restrictive packaging
  • individual skin compatibility

Not every cosmetic product sold in Japan displays its retinol concentration.

Did you know? Check what the “1%” actually refers to

Some products may advertise “1%” when they contain 1% of a premixed raw material or complex that itself contains retinol, rather than 1% pure retinol.

In that situation, the actual concentration of retinol itself may be lower.

When comparing percentages, it is useful to check what exactly the percentage refers to.

Retinol is sensitive to light, oxygen and heat

One of the most important characteristics of retinol is its stability.

Retinol and some other retinoids can be affected by light, oxygen and temperature.

Cosmetic formulations may therefore use technologies such as:

  • light-protective packaging
  • air-restrictive containers
  • encapsulation
  • antioxidant systems
  • stabilised formulations

to help protect the ingredient.

Did you know? Stability matters as much as the number on the label

Research examining commercial cosmetic products has found substantial differences in retinoid stability, with degradation occurring under conditions such as light exposure and elevated temperature.

This means that in addition to the concentration at the time of manufacture, how the ingredient is stabilised and protected by the packaging is also important.

Follow the product's storage instructions, avoid excessive heat and direct sunlight, and close the packaging properly after use.

How to use retinol skincare products

Retinol products vary in concentration, formulation and recommended use.

Start by checking the manufacturer's recommended amount, frequency and time of application.

A typical routine may involve:

  • cleansing and completing your basic skincare steps
  • applying the retinol product in the order recommended by the manufacturer
  • using a moisturiser where appropriate
  • using sun protection during the day

When beginning a new retinol product, it can be easier to start at a lower frequency and test how your skin responds on a small area, following the product instructions.

Areas around the eyes, corners of the mouth and sides of the nose can sometimes be more sensitive, so check where the individual product is intended to be used.

What is a “retinoid reaction”?

In Japanese beauty media, you may see the term “A反応” (“A reaction”) used when discussing retinol.

It commonly refers to temporary skin responses that can occur after starting retinol or other retinoids, such as:

  • redness
  • dryness
  • flaking
  • stinging
  • itching

“A reaction” is not a formal medical diagnosis. In dermatology, these types of symptoms may be described as retinoid irritation or retinoid dermatitis.

Did you know? With retinol, a comfortable routine matters more than the intensity of irritation

Rather than using the strength of a skin reaction as a measure of effectiveness, it is more practical to follow the product directions and choose a frequency that your skin can tolerate comfortably.

If irritation develops, options may include adjusting the frequency of use or adding more moisturising care.

If pronounced redness, swelling, pain or persistent itching occurs, stop using the product and seek medical advice if needed.

How can retinol be combined with other skincare ingredients?

Retinol can be combined with other skincare ingredients by considering the formulation, concentration and frequency of each product.

Particular care may be useful when combining retinol with:

  • AHA or BHA exfoliating products
  • scrubs or peeling products
  • other high-strength skincare products that may increase irritation

If several active or exfoliating products are part of your routine, it may be easier to alternate days, adjust frequency or introduce products one at a time while monitoring how your skin feels.

Moisturising products can also be useful when dryness occurs during retinol use.

When combining multiple skincare products, check the instructions for each one and adjust the routine according to your skin condition.

Retinol and sun protection

Retinol itself is sensitive to light, which is one reason many retinol products are recommended for evening use.

However, the recommended time of application depends on the individual formulation.

Some products are intended mainly for nighttime use, while others are formulated for use in both morning and evening routines.

Retinoid products can also cause dryness or irritation in some users.

During the day, practical UV-protection measures include:

  • sunscreen
  • hats
  • parasols
  • protective clothing
  • shade

For more information about SPF, PA, UVA, UVB and choosing sunscreen, see: What Is Sunscreen? SPF, PA, UVA, UVB, How to Choose, Apply & Reapply.

What about pregnancy and planning a pregnancy?

Some vitamin A derivatives used as retinoid medicines require particularly careful management during pregnancy.

Topical retinoid medicines are absorbed systemically to a much smaller extent than oral retinoids, but medical and regulatory organisations in several countries recommend avoiding topical retinoid medicines during pregnancy and when planning a pregnancy as a precaution.

This guidance relates specifically to the safety management of retinoids used as medicines.

For cosmetics containing retinol, it is also sensible to check the product label and discuss use with your obstetrician or another qualified healthcare professional if you are pregnant or planning a pregnancy.

During breastfeeding, appropriate use may also depend on the individual product and where it is applied, so check the product instructions and seek professional advice where appropriate.

How to choose a retinol skincare product

When comparing retinol skincare, it is useful to look beyond concentration and consider:

  • which retinoid is used
  • whether the retinol concentration is clearly stated
  • whether a percentage refers to pure retinol or a premixed retinol-containing raw material
  • stabilisation technology and packaging
  • the overall formulation, including moisturising ingredients
  • where the product is intended to be used
  • recommended frequency of use
  • how well the product suits your skin

Because retinol is a relatively delicate ingredient, it is useful to compare the type of retinoid, formulation, packaging and recommended use together rather than relying on one number alone.

Retinol and “wrinkle improvement” claims in Japan

This is an important distinction when looking at retinol skincare sold in Japan.

There is extensive dermatological research on retinoids, but scientific research findings and the efficacy claims legally permitted for cosmetics are separate matters.

Claims permitted for ordinary cosmetics

Ordinary cosmetics in Japan may use claims within the scope permitted by the Ministry of Health, Labour and Welfare, including expressions relating to:

  • providing moisture to the skin
  • conditioning the skin
  • softening the skin
  • giving the skin a feeling of firmness
  • making the skin feel smooth

The expression “makes fine lines caused by dryness less noticeable” may also be used when the effect has been confirmed for the individual product through the appropriate efficacy evaluation testing.

“Improves wrinkles” is an approved quasi-drug claim

In Japan, “improves wrinkles” is not a claim that every ordinary cosmetic containing retinol may automatically use.

There are Japanese quasi-drug products in which pure retinol has been approved as an active ingredient with an authorised wrinkle-improvement claim.

That claim applies within the scope of the approved active ingredient, formulation and efficacy for the specific quasi-drug product.

It is therefore useful to distinguish between:

research investigating the relationship between retinol and wrinkles and whether a particular retinol-containing cosmetic is legally permitted to advertise wrinkle improvement.

Understanding this difference makes it easier to compare ordinary cosmetics and approved quasi-drug products in Japan.

Summary: look beyond concentration to type, formulation and use

Retinol is a vitamin A-derived retinoid that has been studied extensively in skincare and dermatology.

The key points are:

  • Retinol is one form of vitamin A and belongs to the wider retinoid family.
  • A simplified pathway is retinyl esters → retinol → retinal → retinoic acid.
  • Retinol, retinal and tretinoin differ in their properties and regulatory status.
  • Retinol products should be compared by formulation, stabilisation technology, packaging and frequency of use as well as concentration.
  • Redness, dryness and flaking commonly described as an “A reaction” can be managed by adjusting use according to skin tolerance.
  • Information about pores and acne should distinguish pharmaceutical retinoid research from ordinary cosmetic retinol products.
  • If you are pregnant or planning a pregnancy, check the product instructions and discuss retinoid use with a healthcare professional.
  • In Japan, ordinary cosmetic claims are different from the approved “wrinkle improvement” claims of specific quasi-drugs.

Rather than assuming that a stronger concentration is automatically better, it is more useful to consider which retinoid is used, how it is formulated and how frequently the product is intended to be applied.

Using the product according to its directions, supporting the skin with moisturising care and maintaining appropriate UV protection are practical foundations for incorporating retinol into a skincare routine.

Related Articles

Main References

  • Ministry of Health, Labour and Welfare, Japan. Scope of Permitted Cosmetic Efficacy Claims.
  • Japan Cosmetic Industry Association. Guidance on Wrinkle-Related Cosmetic Claims.
  • Japan Cosmetic Industry Association. Guidelines for Appropriate Advertising of Cosmetics and Quasi-Drugs.
  • Mambwe M, et al. Cosmetic retinoid use in photoaged skin: A review of the compounds, their use and mechanisms of action. Int J Cosmet Sci. 2025.
  • Farris P, et al. Efficacy and Tolerability of Topical 0.1% Stabilized Bioactive Retinol for Photoaging. J Drugs Dermatol. 2024.
  • Topical retinoids: Novel derivatives, nano lipid-based carriers, and combinations to improve chemical instability and skin irritation. 2024.
  • Retinoid stability and degradation kinetics in commercial cosmetic products. 2021.
  • American College of Obstetricians and Gynecologists. Skin Conditions During Pregnancy.
  • European Medicines Agency. Updated measures for pregnancy prevention during retinoid use.

Important Information

This article is intended to provide general educational information about retinol, retinoids, vitamin A and skincare.

It is not intended to diagnose, treat, cure or prevent disease, and it does not claim pharmaceutical or quasi-drug efficacy for any particular cosmetic product.

The type of retinol or retinoid, concentration, frequency of use, application area and compatibility with other skincare products vary between products. Always follow the directions and manufacturer guidance for the product you use.

If pronounced redness, swelling, itching, pain or severe flaking occurs, stop using the product. If symptoms persist, consult a dermatologist or another qualified healthcare professional.

If you are pregnant, planning a pregnancy, breastfeeding or receiving treatment for a skin condition, discuss the use of retinoid-containing products with your doctor or pharmacist before use.

Category
Beauty & Skincare

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