Paula's Choice Resist Youth-Extending Daily Hydrating Fluid

DESCRIPTION

What It Does: Provides uva-i protection (340-400nm) critical for photoaging prevention — the only widely available chemical uva-i filter.

Why It's Used: The essential uva-i filter — avobenzone is the only commonly approved chemical filter providing protection in the photoaging-critical 340-400nm range essential for broad-spectrum sunscreen claims.

How It Works: Dibenzoylmethane chromophore absorbs uva-i (λmax 357nm, εmax ~36,000). photodegrades via photoisomerisation requiring photostabilisation (octocrylene, bemotrizinol) for durability.

Typically Found In: Broad-spectrum sunscreens,anti-aging spf products

TECHNICAL DETAILS

Primary Category: Active ingredient – chemical uva-i filter

Secondary Functions: Skin conditioning

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: Up to 5% (eu), 3% (us fda)

SOURCING & ETHICS

Vegan Status: Yes – synthetic

Halal Status: Yes

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Eu max 5%. fda: 3%. ewg score: 2. requires photostabilisation. photoallergy risk in some individuals.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Avobenzone's photodegradation discovery drove development of photostabilisation technology — the period from avobenzone's 1978 introduction to development of effective photostabilisers in the 1990s was marked by sunscreens with inadequate uva durability. bemotrizinol (tinosorb s) development provided the most elegant solution by providing a photostable molecule with equivalent uva coverage.

Last Verified: Cosing database,fda uv filter otc monograph,shaath sunscreen photostabilisation review

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Provides silicone-characteristic silky feel and skin protection with adjustable viscosity.

Why It's Used: The benchmark cosmetic silicone – sets the gold standard for silky application feel, spreadability, and skin protection in virtually all skin care categories.

How It Works: Polydimethylsiloxane chain flexibility provides extremely low surface tension and high spreadability. inert si-o backbone provides chemical stability and excellent skin tolerance. occlusive film formation reduces tewl. higher viscosity grades provide more intense conditioning.

Typically Found In: Moisturizers,foundations,primers,sunscreens – nearly universal

TECHNICAL DETAILS

Primary Category: Functional ingredient – polydimethylsiloxane

Secondary Functions: Barrier sealing,softening

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: 0.1%–30%

SOURCING & ETHICS

Vegan Status: Yes – synthetic

Halal Status: Yes

Source Notes: Plant-derived, synthetic or animal-derived. verify source.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 1/5 – low; formulation-dependent

Sensitivity Concerns: Non-irritating.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Excellent safety profile. ewg score: 1.

Works Well With: Humectants,ceramides,actives as carrier

Avoid Combining With: No significant incompatibilities

SCIENTIFIC NOTE

Dimethicone's exceptional silky feel arises from its very low intermolecular attractive forces (weak van der waals forces due to non-polar methyl groups) that allow silicone chains to slide freely over skin. the coefficient of kinetic friction for pdms against skin (~0.04) is among the lowest of any cosmetic material – explaining why even small amounts transform product feel.

Last Verified: Cosing database,cir safety assessment

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Glycerin pulls water from the environment and deeper skin layers into the outer skin layer (epidermis), boosting moisture levels and keeping skin soft, smooth, and plump.

Why It's Used: It is used in virtually every moisturizer, serum, and cleanser because it is highly effective at hydrating skin, is well-tolerated by all skin types, and enhances the texture and spreadability of formulations.

How It Works: As a humectant, glycerin forms hydrogen bonds with water molecules, trapping them in the skin. it also reinforces the skin barrier by integrating into lipid structures between skin cells.

Typically Found In: Moisturizers,serums,cleansers,toners,sheet masks,sunscreens,body lotions,shampoos,conditioners

TECHNICAL DETAILS

Primary Category: Humectant

Secondary Functions: Skin barrier support,emollient,solvent

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: 1%–30% (typical: 3–10%)

SOURCING & ETHICS

Vegan Status: Yes – plant-derived (coconut, soy, palm) or synthetic

Halal Status: Yes – when plant-derived or synthetic; verify source with supplier

Source Notes: Derived from plant oils via hydrolysis or saponification; synthetic versions also available. palm-derived glycerin carries sustainability concerns.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low; non-irritating at all standard concentrations

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Extremely rare allergic reactions; generally safe for all skin types including sensitive and baby skin

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Widely recognized as safe. ewg hazard score: 1. no significant concerns for irritation, sensitization, or toxicity at typical concentrations (up to 50%).

Works Well With: Hyaluronic acid,ceramides,niacinamide,panthenol,urea,peptides,retinol,ahas/bhas

Avoid Combining With: No known incompatibilities at standard concentrations

SCIENTIFIC NOTE

Glycerin is an endogenous skin component found naturally in the stratum corneum. aquaporin-3 channels in keratinocytes facilitate glycerin transport, making it integral to natural skin hydration pathways.

Last Verified: Cosing database,cir safety assessment,ewg skin deep,inci decoder

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Provides the most widely used uvb chemical filtration with light, elegant aesthetics.

Why It's Used: The global uvb standard — octyl methoxycinnamate's combination of potent uvb absorption, light texture, and global approval makes it the most-used chemical uvb filter worldwide.

How It Works: Trans-cinnamate chromophore absorbs uvb at λmax 308nm (εmax ~24,000 l/mol·cm). undergoes trans-cis photoisomerisation reducing uv protection over time — requires photostabilisation with avobenzone or octocrylene. oil-soluble for elegant formulation.

Typically Found In: Sunscreens,foundation with spf,tinted moisturisers

TECHNICAL DETAILS

Primary Category: Active ingredient – chemical uvb filter

Secondary Functions: Skin conditioning

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: Up to 10% (eu), 7.5% (us fda)

SOURCING & ETHICS

Vegan Status: Yes – synthetic

Halal Status: Yes

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Eu max 10%. aquatic toxicity/coral reef concerns; hawaii and some us states restrict omc. requires photostabilisation for durable spf. ewg score: 5.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Omc's trans-cis photoisomerisation (absorbing uv → converting trans to less-absorbing cis form) was identified as the mechanism for sunscreen product spf decay after uv exposure. this photodegradation led to development of octocrylene and avobenzone photostabilisation strategies — a pharmacokinetic discovery that fundamentally changed sunscreen formulation science.

Last Verified: Cosing database,fda uv filter otc monograph,eu cosmetics annex vi

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Absorbs uva (320–400 nm) and/or uvb (290–320 nm) photons with a high molar extinction coefficient, dissipates absorbed energy as vibrational heat, and contributes to the formulation's spf and critical wavelength.

Why It's Used: Organic uv filters are selected for their high molar extinction coefficient (>10,000 l/mol/cm for most commercial filters), specific spectral coverage complementing other filters in the system, and photostability under prolonged uv exposure.

How It Works: Aromatic π→π* and n→π* electronic transitions absorb uv photons exciting the chromophore to a singlet excited state (s₁). ultra-fast internal conversion (10⁻¹²–10⁻¹¹ s) dissipates excitation energy as heat rather than photochemical reactions, returning the molecule to the ground state for continued absorption.

Typically Found In: Sunscreens,spf formulas

TECHNICAL DETAILS

Primary Category: Active ingredient – cosmetic active

Secondary Functions: Skin conditioning

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: Check local sunscreen limits

SOURCING & ETHICS

Vegan Status: Yes

Halal Status: Yes

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Good safety profile at recommended concentrations. ewg score: 1–2.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Organic uv filter photostability varies significantly — avobenzone degrades rapidly alone but is stabilised by octocrylene (energy quenching) or triazine-class filters (direct stabilisation). filter combination selection must account for photostabilisation requirements of each component.

Last Verified: Cosing database,organic uv filter photostability combination review

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Provides uvb-uva-ii uv protection and essential avobenzone photostabilisation.

Why It's Used: The essential combination partner — octocrylene's dual uv filter + avobenzone photostabilisation function makes it virtually irreplaceable for durable broad-spectrum chemical sunscreens requiring uva-i coverage.

How It Works: Cyanocinnamate chromophore absorbs uvb-uva-ii (λmax 303nm). triplet energy transfer from excited avobenzone to octocrylene photostabilises avobenzone (>90% efficiency at 3:1 avobenzone:octocrylene ratio). hydrophobic character enhances water resistance.

Typically Found In: Broad-spectrum sunscreens,avobenzone-containing formulas

TECHNICAL DETAILS

Primary Category: Active ingredient – uv filter and photostabiliser

Secondary Functions: Skin conditioning

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: Up to 10% (eu), 10% (us fda)

SOURCING & ETHICS

Vegan Status: Yes – synthetic

Halal Status: Yes

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Eu max 10%. fda: 10%. ewg score: 3. recent benzophenone impurity concerns from aged product hydrolysis under study.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Octocrylene's triplet energy transfer photostabilisation of avobenzone operates via a dexter electron exchange mechanism: excited-state avobenzone (triplet) transfers excitation energy to octocrylene via orbital overlap, allowing avobenzone to return to its ground state uv-absorbing form without photodegradation. this energy transfer is only efficient at close molecular proximity — requiring intimate mixing of the two compounds in the formulation oil phase.

Last Verified: Cosing database,fda uv filter otc monograph,sccs octocrylene opinion

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Prevents microbial contamination and spoilage in cosmetic formulations.

Why It's Used: The benchmark cosmetic preservative – eu-permitted up to 1%, effective against virtually all cosmetically relevant microorganisms, and excellent tolerability.

How It Works: Phenol ring provides broad antimicrobial activity via disruption of bacterial and fungal cell membranes and inhibition of enzymatic activity. effective against gram-positive and gram-negative bacteria, yeasts (candida), and molds (aspergillus). activity ph range: 3-9.

Typically Found In: All cosmetic formulations as primary preservative

TECHNICAL DETAILS

Primary Category: Functional ingredient – broad-spectrum preservative

Secondary Functions: Skin conditioning

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: 0.1%–1% (eu max 1%)

SOURCING & ETHICS

Vegan Status: Yes – synthetic

Halal Status: Yes

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Eu cosmetics regulation max 1%. sccs assessed as safe at ≤1%. avoid use around eyes in baby products per some country regulations. ewg score: 4.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Phenoxyethanol's widespread adoption as the primary cosmetic preservative followed the phaseout of parabens from many formulations in the 2000s-2010s. despite having a comparable or better safety profile to parabens, it is often cited in 'free-from' formulations – a consumer perception issue rather than a scientific safety concern.

Last Verified: Cosing database,sccs opinion on phenoxyethanol,cir safety assessment

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Delivers characteristic cosmetic function at recommended use concentration.

Why It's Used: Selected for functional contribution and formulation compatibility supported by cosmetic science and regulatory safety data.

How It Works: Works through the mechanism of its molecular class — physicochemical or biological interaction with skin proteins, lipids, or receptors as documented in peer-reviewed cosmetic literature.

Typically Found In: Skin care formulations

TECHNICAL DETAILS

Primary Category: Active ingredient – cosmetic active

Secondary Functions: Skin conditioning

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: 0.1%–10%

SOURCING & ETHICS

Vegan Status: Conditional

Halal Status: Yes

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Good safety profile at recommended concentrations. ewg score: 1–2.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Silica has an established safety and efficacy profile within the cosmetic regulatory framework at standard use concentrations.

Last Verified: Cosing database,silica technical literature

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Tocopherol neutralizes free radicals that damage skin cells, protects cell membranes from lipid peroxidation, moisturizes, and helps maintain a healthy skin barrier.

Why It's Used: It is used as both a skin-active antioxidant and a formulation stabilizer (preventing oxidation of other ingredients). it has decades of safety and efficacy evidence and works synergistically with vitamin c.

How It Works: As a chain-breaking antioxidant, tocopherol donates hydrogen atoms to interrupt lipid peroxidation chain reactions. it is regenerated by vitamin c (ascorbic acid) in the vitamins c+e antioxidant cycle, creating a more durable antioxidant defense.

Typically Found In: Moisturizers,serums,oils,sunscreens,eye creams,lip balms,antioxidant formulations,haircare products

TECHNICAL DETAILS

Primary Category: Active ingredient – antioxidant/vitamin e

Secondary Functions: Emollient,formulation stabilizer,barrier support

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: 0.1%–1% (typical: 0.1–0.5% as active; higher as formulation antioxidant)

SOURCING & ETHICS

Vegan Status: Yes – plant-derived (soybean, sunflower, wheat germ oil) or synthetic

Halal Status: Yes – plant-derived or synthetic

Source Notes: Natural d-alpha-tocopherol is derived from plant oils and is more bioactive. synthetic dl-alpha-tocopherol is less expensive. tocopherol acetate (tocopheryl acetate) is the more stable ester form.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low; rare contact sensitivity reported

Comedogenicity Rating: 2/5 – mildly comedogenic at higher concentrations; formulation-dependent

Sensitivity Concerns: A small percentage of people report contact sensitization to tocopherol, particularly with leave-on products. comedogenicity risk is higher in oil-heavy formulations.

Safe for Sensitive Skin: Generally yes; perform patch test if history of vitamin e sensitivity

SAFETY & COMPATIBILITY

Safety Profile: Very safe; widely used. ewg hazard score: 2–3 (depending on concentration). no significant systemic concerns from topical use.

Works Well With: Ascorbic acid (vitamin c) – synergistic antioxidant pair,ferulic acid – stabilizes and boosts both c and e,ceramides,spf,retinol

Avoid Combining With: Very high concentrations of benzoyl peroxide may oxidize tocopherol; potential comedogenicity concerns in acne-prone skin when in heavy oil bases

SCIENTIFIC NOTE

The combination of vitamin c, vitamin e, and ferulic acid (the 'ce ferulic' formulation) provides fourfold photoprotection against uv-induced free radical damage – a synergy documented in landmark research by pinnell et al.

Last Verified: Cosing database,cir safety assessment,pinnell et al. (2005) journal of investigative dermatology,efsa panel on food additives

Primary Sources: 2026-03-12

DESCRIPTION

What It Does: Provides the universal solvent and vehicle for water-soluble actives and the continuous phase of all o/w emulsions.

Why It's Used: The most essential cosmetic ingredient — aqua (water) is listed first on virtually all water-containing cosmetic inci labels as the highest-concentration ingredient, serving as the foundation of the global cosmetics industry.

How It Works: Acts as solvent for all water-soluble ingredients (glycols, amino acids, water-soluble actives). forms the continuous external phase of o/w emulsions (lotions, creams, serums). provides aqueous environment for enzymatic and chemical reactions between actives. ph adjustment medium.

Typically Found In: Virtually all cosmetic products — the most universal cosmetic ingredient globally

TECHNICAL DETAILS

Primary Category: Functional ingredient – water

Secondary Functions: Skin conditioning

Application Areas:

Facial Skincare

Body Care

Hair Care

Beard Care

Color Cosmetics (Makeup)

Dietary/Oral Supplements

Typical Concentration Range: Varies widely — up to 95% in some toners and serums

SOURCING & ETHICS

Vegan Status: Yes – water (deionised/purified)

Halal Status: Yes

Source Notes: Cosmetic-grade water is purified (deionised, distilled, or ro filtered) to prevent mineral content interference with formulation stability. european pharmacopoeial water (aqua purificata ph. eur.) is the quality standard for pharmaceutical and high-end cosmetic formulations.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – non-irritant

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Good safety profile at recommended concentrations. ewg score: 1–2.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Water's position as the first inci ingredient on most cosmetic labels reflects the regulatory requirement to list ingredients in descending concentration order — meaning water is the most abundant ingredient in the majority of cosmetic products. the fundamental role of water as the universal cosmetic solvent and vehicle makes it simultaneously the most important cosmetic ingredient and the one that requires the most sophisticated formulation chemistry to control — every emulsifier, thickener, preservative, and ph adjuster exists primarily to manage water's interaction with other ingredients in formulation.

Last Verified: Cosing database,eu cosmetics regulation 1223/2009 inci requirements,ph. eur. aqua purificata monograph

Primary Sources: 2026-03-12