Y Theorem Repair Light Serum NAC Y²

111Skin

Where to buy Possibly in stock

About this product

The 111Skin Y Theorem Repair Light Serum NAC Y² is a serums, essence, ampoule. Our analysis of its 26 ingredients (18 low-risk) rates it Excellent (98/100). Based on its ingredients, it looks well-suited to oily / acne-prone skin. Heads up: it contains fragrance, which can irritate sensitive or reactive skin.

Vegan-friendly Reef-safe

Summarised from our ingredient analysis — not brand marketing copy.

At a glance

Type
Serums, Essence, Ampoules
Ingredients
26
Low-risk
18
Fragrance
Contains fragrance
Origin
United Kingdom
Data updated
May 2026

The evidence

Quick Product Notes

Paraben-Free Sulfate-Free Alcohol-Free Silicone-Free EU Allergen-Free Fungal Acne (Malassezia) Safe

Notable Effects & Ingredients

No Notable Effects & Ingredients

Ingredients Related to Skin Types

Good   Bad — tap a skin type to see which ingredients · estimated from ingredient functions
Dry Skin 2/3
Good for dry skin
Glycerin Propylene Glycol
Caution for dry skin
Glycerin Alcohol Sodium Hydroxide
Oily/Acne-Prone Skin 2/0
Good for oily/acne-prone skin
Sodium Ascorbyl Phosphate Alcohol
Sensitive Skin 3/8
Good for sensitive skin
Sodium Ascorbyl Phosphate Acetyl Cysteine Glycerin
Caution for sensitive skin
Glycerin Propylene Glycol Citric Acid Alcohol Sodium Benzoate Potassium Sorbate Benzyl Alcohol Thiamine HCl

Ingredients list

26 total
Lower hazard (1) Higher hazard (5)
All26 Skin Conditioning15 Fragrance9 Solvent5 Masking5 Hair Conditioning4 Humectant4 Antioxidant3 Preservative3
EWG CIR Ingredient Name & Cosmetic Functions Notes
1
Water
(Solvent)
2
A
Glycerin
(Denaturant, Fragrance, Hair Conditioning, Humectant, Oral Care Agent, Oral Health Care Drug, Skin Protecting, Viscosity Decreasing Agent, Perfuming, Solvent)
Good for Dry Skin
Good for Dry Skin
Fungal Acne
Fungal Acne Trigger
2
Alcohol
(Antifoaming Agent, Antimicrobial, Astringent, Masking, Solvent, Viscosity Controlling)
Bad for Dry Skin
Bad for Dry Skin
Bad for Sensitive Skin
Bad for Sensitive Skin
5
A
Benzyl Alcohol
(External Analgesic, Fragrance, Oral Health Care Drug, Preservative, Solvent, Viscosity Decreasing Agent, Masking)
Allergens
Allergens
1
3
Aloe Barbadensis Extract
(Skin Conditioning)
1
A
Calendula Officinalis Extract
(Skin Conditioning)
Good for Oily Skin
Good for Oily Skin
1
A
Carbomer
(Emulsion Stabilising, Viscosity Increasing Agent, Gel Forming, Viscosity Controlling)
3
B
Propylene Glycol
(Fragrance, Humectant, Skin Conditioningagent Miscellaneous, Solvent, Viscosity Decreasing Agent, Skin Conditioning, Viscosity Controlling)
Good for Dry Skin
Good for Dry Skin
3
B
Sodium Hydroxide
(Denaturant, Ph Adjuster, Buffering Agent)
Aesculus Hippocastanum Seed Extract
(Skin Conditioning)
1
A
Sodium Ascorbyl Phosphate
(Antioxidant)
1
A
Panthenol
(Antistatic Agent, Hair Conditioning, Skin Conditioning)
Good for Dry Skin
Good for Dry Skin
1
A
Niacinamide
(Hair Conditioning, Skin Conditioning, Smoothing)
Thiamine HCl
(Masking, Skin Conditioning)
1
Riboflavin
(Cosmetic Colorant, Skin Conditioning)
1
Pyridoxine
(Hair Conditioning, Skin Conditioning, Antistatic Agent)
1
Cyanocobalamin
(Skin Conditioning)
glycyrrhiza glabra root extract
(Bleaching, Perfuming, Skin Conditioning, Skin Conditioning Emollient, Smoothing, Soothing)
prunus armeniaca kernel oil
(Fragrance, Skin Conditioning)
1
B
Acetyl Cysteine
(Antioxidant, Skin Conditioning)
TOCOPHEROL
(Antioxidant, Fragrance, Skin Conditioning)
Olus oil
(Skin Conditioning Emollient)
2
A
Citric Acid
(Chelating Agent, Fragrance, Ph Adjuster, Buffering Agent, Masking)
Bad for Sensitive Skin
Bad for Sensitive Skin
3
A
Sodium Benzoate
(Fragrance, Preservative, Anticorrosive, Masking)
3
A
Potassium Sorbate
(Fragrance, Preservative)
PARFUM
(Fragrance, Perfuming)

My Ingredient Notes

No personal ingredient notes yet. Save ingredients to your profile to get good/bad alerts here.

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Key ingredients

Antioxidants
Shields skin from free radical damage.
Vitamin C
Brightens, evens tone, and supports collagen.
Vitamin E
Protects skin and soothes irritation.
Niacinamide
Strengthens, smooths, and brightens skin.

Benefits

Redness ReducingSoothes visible redness and calms irritation.
HydratingBoosts hydration and relieves dry, tight skin.
Reduces IrritationEases discomfort and supports skin resilience.
Scar HealingImproves the look of marks and scars.
Barrier RepairStrengthen and restore your skin's natural barrier.
BrighteningRestores radiance to dull, tired skin.
Dark SpotsFades dark spots for even skin tone.
Anti-AgingSoftens lines and helps skin look youthful.

Concerns

Contains eu allergen
Not fungal acne (malassezia) safe
May not suit dry skin
May not suit sensitive skin

Ingredients explained

Water
Solvent
Low-hazard ingredient.Read moreShow less
EWG 1 Solvent
Aloe Barbadensis Extract
Skin conditioning
Low-to-moderate hazard.Read moreShow less
EWG 1–3 Skin conditioning
Carbomer
Emulsion stabilising, Viscosity increasing agent
Low-hazard ingredient.Read moreShow less
EWG 1 CIR A Emulsion stabilisingViscosity increasing agentGel formingViscosity controlling
Sodium Hydroxide
Denaturant, Ph adjuster
Low-to-moderate hazard.Read moreShow less
EWG 3 CIR B DenaturantPh adjusterBuffering agent
Aesculus Hippocastanum Seed Extract
Skin conditioning
Limited public safety data.Read moreShow less
EWG N/A Skin conditioning
Sodium Ascorbyl Phosphate
Antioxidant
Low-hazard ingredient.Read moreShow less
EWG 1 CIR A Antioxidant
Niacinamide
Hair conditioning, Skin conditioning
Low-hazard ingredient.Read moreShow less
EWG 1 CIR A Hair conditioningSkin conditioningSmoothing
Thiamine HCl
Masking, Skin conditioning
Limited public safety data.Read moreShow less
EWG N/A MaskingSkin conditioning
Riboflavin
Cosmetic colorant, Skin conditioning
Low-hazard ingredient.Read moreShow less
EWG 1 Cosmetic colorantSkin conditioning
Pyridoxine
Hair conditioning, Skin conditioning
Low-hazard ingredient.Read moreShow less
EWG 1 Hair conditioningSkin conditioningAntistatic agent
Cyanocobalamin
Skin conditioning
Low-hazard ingredient.Read moreShow less
EWG 1 Skin conditioning
glycyrrhiza glabra root extract
Bleaching, Perfuming
Limited public safety data.Read moreShow less
EWG N/A BleachingPerfumingSkin conditioningSkin conditioning emollientSmoothingSoothing
prunus armeniaca kernel oil
Fragrance, Skin conditioning
Limited public safety data.Read moreShow less
EWG N/A FragranceSkin conditioning
Acetyl Cysteine
Antioxidant, Skin conditioning
Low-hazard ingredient.Read moreShow less
EWG 1 CIR B AntioxidantSkin conditioning
TOCOPHEROL
Antioxidant, Fragrance
Limited public safety data.Read moreShow less
EWG N/A AntioxidantFragranceSkin conditioning
+ 4 more — see the full ingredients list above
Glycerin
Denaturant, Fragrance
Low-hazard ingredient.Read moreShow less
EWG 2 CIR A DenaturantFragranceHair conditioningHumectantOral care agentOral health care drugSkin protectingViscosity decreasing agentPerfumingSolvent Good for Dry SkinFungal-acne trigger
Alcohol
Antifoaming agent, Antimicrobial
Causes moisture evaporation - prone to dry out skinRead moreShow less
EWG 2 Antifoaming agentAntimicrobialAstringentMaskingSolventViscosity controlling Bad for Dry SkinBad for Sensitive Skin
Benzyl Alcohol
External analgesic, Fragrance
Moderate-hazard ingredient.Read moreShow less
EWG 5 CIR A External analgesicFragranceOral health care drugPreservativeSolventViscosity decreasing agentMasking Allergens
Calendula Officinalis Extract
Skin conditioning
Low-hazard ingredient.Read moreShow less
EWG 1 CIR A Skin conditioning Good for Oily Skin
Propylene Glycol
Fragrance, Humectant
Low-to-moderate hazard.Read moreShow less
EWG 3 CIR B FragranceHumectantSkin-conditioningagent - miscellaneousSolventViscosity decreasing agentSkin conditioningViscosity controlling Good for Dry Skin
Panthenol
Antistatic agent, Hair conditioning
Low-hazard ingredient.Read moreShow less
EWG 1 CIR A Antistatic agentHair conditioningSkin conditioning Good for Dry Skin
Citric Acid
Chelating agent, Fragrance
Skin irritation can occur at high concentrationRead moreShow less
EWG 2 CIR A Chelating agentFragrancePh adjusterBuffering agentMasking Bad for Sensitive Skin

How to use

How to use

  • 1 Where it fits: Apply after toner and before moisturiser — thinnest to thickest.
  • 2 Morning works well: Antioxidants like vitamin C pair well with daytime use under sunscreen.

General guidance from this product's category and active ingredients — always follow the directions on the package.

Trust & honesty

Effective levels — general guide

The concentrations these actives are typically effective at in research — not a measurement of this product.

Vitamin C (ascorbic) 5–20%

L-ascorbic acid is usually used at 5–20% (around 10–15% is common). Above ~20% adds little and tends to irritate more; it also needs a low pH to work.

Sodium Ascorbyl Phosphate

Niacinamide 2–5% (up to 10%)

Most research uses 2–5%; some formulas go to 10%. Very high levels can cause flushing in sensitive skin.

Niacinamide

INCI lists don't disclose amounts, and we don't claim to know this product's levels — these are the ranges these ingredients are usually effective at, so you can tell a real formula from "fairy-dusting" a marketed active. How we estimate this.

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