Its role:
Shortens the skin cell regeneration cycle, mimicking skin exfoliation
Increases collagen production
Reduces skin blemishes
Its keratolytic action removes dead cells, unclogs pores and diminishes acne.
Concentration ranges from 0.1% to 1%
This active ingredient is irritating and dries out the skin at first. A period of tolerance is necessary at first, so begin application gradually.

Find out more about retinol and the best retinol cosmetics

Pure Vitamin C: L ascorbic acid

Its role:
Pure vitamin C is an anti-oxidant
It is essential for collagen production and preserves its integrity.
It combats hyperpigmentation,
Particularity: it's an unstable molecule that can oxidize, is hydrophilic and requires an acid PH to penetrate the skin.
Average concentration ranges from 5% to 20%.
It is an irritant "because of its acid PH".
Vitamin C derivatives
There are plenty of them:
Their role: They fight stains
They can be hydrophobic or hydrophilic
They are non-irritating

Find out more about vitamin C and the best vitamin C cosmetics

Niacinamide: Vitamin B3

Its role:
Niacinamide is an antioxidant
It combats hyperpigmentation by reducing the transfer of melanin from melanocytes to the skin's surface.
It increases the production of ceramides, an important component of our skin barrier.
It increases collagen production
Reduces sebum production
It is a non-irritating active ingredient, but can sometimes cause redness.
Average concentration ranges from 2% to 20%
It is non-irritating

Find out more about niacinamide and the best niacinamide cosmetics

Azelaic acid:

Azelaic acid is useful in the treatment of acne, skin blemishes and facial redness. It has anti-inflammatory and anti-bacterial properties, and regulates keratinocyte proliferation, helping to combat blemishes.
It is not slightly irritating

Find out more about azelaic acid and the best azelaic acid products

Ingredient families:

Scrubs:

Alpha hydroxy acid:
Glycolic acid is one of the most powerful exfoliants.
Lactic acid is an exfoliant and humectant, ideal for dry skin.
They are irritating

Beta hydroxy acid:
Salicylic acid is an exfoliant that acts on pores, is anti-inflammatory and ideal for oily skin.
They are irritating
Poly hydroxy acid:
They are gentle exfoliants that can be useful for anti-aging, fighting acne, etc...
Lactobionic acid
Gluconolactone

Find out more about exfoliating acids and exfoliation

Peptides:

Peptides have multiple actions and are very numerous.
Certain peptides boost collagen production
Others have a "botox like" effect by reducing muscle contraction.
They can have a very useful draining action on the eye contour area.
Most of them have a moisturizing action.

Copper peptide is a peptide widely studied in anti-aging, as it increases collagen production.
They are non-irritating

Find out more about peptides and the best peptide cosmetics

ANTIOXIDANTS:

L-ascorbic acid, or pure vitamin C, vitamin E, also known as tocopherol, ferulic acid, Q10 coenzyme, lipoic acid, superoxide dismutase
Polyphenols, which are notably present in plant extracts, the resveratrolflavonoids, green tea, ginseng, turmeric.
They are non-irritating, except for pure vitamin C

Moisturizing and nourishing ingredients

Moisturizing ingredients fall into 3 categories:

Humectants:

They attract water to the skin's surface and epidermis, the best-known humectants:
Glycerin is a fairly small molecule, with a molecular weight of 92, which enables it to attract water to the deep layer of the epidermis.
Hyaluronic acid is the star humectant, as the pharmaceutical industry plays on the confusion between cosmetics and aesthetic medicine. Its weight is very significant, ranging from 20,000 to over 2 million. It can attract more than 100 times its own weight in water, making it ideal for moisturizing the skin's surface.

Find out more about hyaluronic acid and the best hyaluronic acid cosmetics

Urea, an interesting humectant, becomes keratolytic in high concentrations.
I mentioned lactic acid above as an exfoliant.
Sugars: The various sugars are humectants
Amino acids: they have strong hydrating properties

Emollients:

They repair our skin barrier, filling the spaces between corneocytes in the stratum corneum. The main emollients are :

Ceramides: Naturally present in the most superficial part of our skin, ceramides are part of the intercellular lipid cement. The CERAVE brand takes its name from ceramides, which are present in all its products.

Vegetable oils: rapeseed oil, sunflower oil, etc. are excellent emollients.

Marula oil is present in all Drunk Elephant products, and legend has it that elephants who eat a lot of Marula become a little drunk.

Squalane: A major ingredient in cosmetics, an American brand uses it in all its "Bioscance" products.

Triglycerides: Triglycerides are emollients widely used in cosmetics.

Occlusives:

They create a protective barrier around the skin, preventing water from evaporating. Dry skin loves them, as they create a kind of protective film and limit insensible water loss.
Mineral oils: Vaseline and paraffin are very powerful occlusives derived from petroleum.
Shea butter: a very useful occlusive agent
Beeswax: often found in sticks or lip balms
Silicones: These can be considered light occlusives, reducing water loss by only 20 to 30%, which makes them interesting for combination to oily skin.
Generally speaking, serums and lotions contain a lot of humectants, few emollients and no occlusives.
Creams can contain all 3 forms of moisturizer, and the proportion varies according to the skin type for which they are intended.
Balms contain many emollients and occlusives and few humectants.

INGREDIENTS BY SKIN CONDITION:

ANTI-WRINKLE:
Collagen-boosting active ingredients:
Retinol, Vitamin C, Peptides, Niacinamide, Exfoliants
Moisturizing active ingredients to reduce dehydration wrinkles
ANTI-AGEING:
Anti-oxidants and all anti-wrinkle active ingredients: Retinol, Vitamin C, Peptides, Niacinamide, Exfoliants
EYE CONTOURS / DARK CIRCLES:
Antioxidants: protect sensitive eyelid skin from free radicals. Some plant antioxidants, such as green tea, have draining properties.
Caffeine: Known for its draining action
Retinoids: firm the skin of the eyelids
Peptides: They have draining and moisturizing properties, and can also reduce dynamic wrinkles and protect the skin's elastin and collagen.
Moisturizers: It's important to moisturize the skin, but beware of occlusive ingredients such as mineral oils, which can cause millium grains.
ANTI-ACNE:
Anti-acne active ingredients include retinol, azelaic acid, salicylic acid and niacinamide.
BLACK POINTS:
Effective ingredients against blackheads: Salicylic acid, exfoliants, retinol, niacinamide and effective facial cleansers.
ANTI-SPOT:
Alpha arbutin, tranexamic acid, thiamidol, viniferin, hydroquinone "banned from over-the-counter sale in France", vitamin C derivatives
Multi-functional active ingredients: pure vitamin C, retinol and azelaic acid
REDNESS:
Azelaic acid:
Tranexamic acid
Soothing active ingredients:
Centella asiatica:
Licorice extracts:
Niacinamide:
Aloe vera:
Allantoine:

Cleaning ingredients: Surfactants

Cleansing ingredients are also known as surfactants. They are ingredients made up of two parts, one that is attracted to fat and one that is attracted to water. Surfactants can therefore bind substances that don't mix, such as water and fat.

In cosmetics, they are used in cleansers of course, but also in creams as emulsifying agents to link hydrophilic and hydrophobic elements.
Sodium lauryl sulfate is a surfactant to be avoided, as it is too aggressive and will damage your skin barrier by degrading your corneocytes and intercellular lipids.
Soap: Unfortunately, soap is very aggressive on the skin, as its PH is too basic, whereas our skin's PH is slightly basic. Soaps generally remove the skin's good lipids and are too aggressive.

Sun filters:

There are two types of sunscreen: mechanical and chemical.
Physical filters:
Zinc oxide
Titanium dioxide
Organic" chemical filters:

AMILOXATE: ISOAMYL P-METHOXYCINNAMATE
AVOBENZONE: BUTYL METHOXYDIBENZOYLMETHANE
BISDISULIZOLE :DISODIUM PHENYL
ENZACAMENE: 4-METHYLBENZYLIDENE CAMPHOR
HOMOSALATE: HOMOMENTHYL SALICYLATE
MEXORYL SL: BENZYLIDENE CAMPHOR SULFONIC ACID
MEXORYL SO: CAMPHOR BENZALKONIUM METHOSULFATE
MEXORYL SX: TEREPHTHALYLIDENE DICAMPHOR SULFONIC ACID
MEXORYL SW: POLYACRYLAMIDOMETHYL BENZYLIDENE CAMPHOR
MEXORYL XL: DROMETRIZOLE TRISILOXANE
OCTINOXATE / UVINUL MC 80: ETHYLHEXYL METHOXYCINNAMATE
OCTISALATE: ETHYLHEXYL SALICYLATE
OCTOCRYLENE / UVINUL N539T: OCTOCRYLENE
OCTYLTRIAZONE / UVINUL T150: ETHYLHEXYL TRIAZONE
OXYBENZONE: BENZOPHENONE-3
PADIMATE O: ETHYLHEXYL DIMETHYL PABA
POLYSILICONE-15: DIMETHICONE DIETHYL BENZYLMALONATE
SULISOBENZONE: BENZOPHENONE-4; BENZOPHENONE-5
TINOSORB A2B: TRIS-BIPHENYL TRIAZINE / TRIS- BIPHENYL TRIAZINE (NANO)
TINOSORB M: METHYLENE BIS-BENZOTRIAZOLYL TETRAMETHYLBUTYLPHENOL
TINOSORB S / BEMOTRIZINOL: BIS-ETHYLHEXYLOXYPHENOL METHOXYPHENYL TRIAZINE
TRIASORB: PHENYLENE BIS-DIPHENYLTRIAZINE
UVASORB HEB: DIETHYLHEXYL BUTAMIDO TRIAZONE
UVINUL A PLUS: DIETHYLAMINO HYDROXYBENZOYL HEXYL BENZOATE
UVINUL P 25: PEG-25 PABA

Conservatives:

Phenoxyethanol

Ingredients suspected of being endocrine disruptors