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Formulating Forum: Climate-Responsive Sun Protection and Eco-friendly Water Resistance

Formulating Forum: Climate-Responsive Sun Protection and Eco-friendly Water Resistance

Industry News Tracker | Miriam Deola, Nicola Lionetti and Francesca Zaros | Cosmetics & Toiletries | March 1, 2026
Read Original Full Article at Cosmetics & Toiletrie

Executive Brief

This article from Labanalysis Life Science (Milan) outlines formulation strategies for climate-responsive sunscreens that maintain protection under heat, humidity, pollution and arid conditions while reducing environmental impact. Beyond broad-spectrum protection (UVA/UVB/HEV/IR) and water/sweat resistance, the authors emphasise minimalist, moisturising textures, antioxidant activity and the use of “ocean‑friendly” UV filters and bio-based film formers. Two case studies – a sprayable SPF 30 oil‑in‑water (O/W) emulsion and an SPF 20 sunscreen oil – show how acrylate polymers can be partially replaced with sebacic-acid–based and polyglyceryl ester film formers, achieving ISO 16217:2020 and ISO 18861:2020 water-resistance requirements with carefully optimised polymer combinations.

Keywords: Climate-Responsive Sunscreens, Eco-friendly Film Formers, Sebacic Acid Polymers, Water Resistance, ISO 16217, ISO 18861.

Technical Intelligence

1. Core Technology / Process

  • Climate-responsive design: Sunscreens are formulated to cope with high temperatures, humidity, urban pollution and dryness, maintaining protection and comfort across climates.
  • Functional requirements:
    • Broad-spectrum protection covering UVA, UVB, high-energy visible (HEV) and infrared (IR) radiation.
    • Water and sweat resistance for real‑world use.
    • Light, moisturising textures plus antioxidant activity to counter free-radical damage from heat and smog.
  • Sustainability principles:
    • Preference for minimalist formulas with multitasking ingredients.
    • Selection of “ocean‑friendly” UV filters to limit reef impact.
    • Use of naturally derived, biodegradable water-resistant polymers and low‑impact manufacturing (renewable energy, reduced water and waste).

2. Key Ingredients / Specifications

Eco-friendly SPF boosters

  • Cyanobacteria (blue‑green algae): Produce UV‑absorbing pigments scytonemin and mycosporine-like amino acids (MAAs) in response to UV, offering natural photoprotection and antioxidant benefits.
  • Propolis: Provides antioxidant and soothing effects and can boost SPF synergistically with UV filters.
  • Lichen-derived usnic acid: A dibenzofuran derivative showing in vivo UVB protection comparable to octocrylene, positioning it as a potential natural SPF booster.

Eco-friendly film formers

  • Natural polymers: Starches, alginates and chitosan are cited as sustainable options to replace synthetic acrylate-based film formers.
  • Sebacic acid chemistry:
    • Long-chain aliphatic diacid derived from castor oil (renewable).
    • Provides hydrophobicity and excellent polycondensation behaviour for long-lasting cosmetic films.

3. Case Study 1 – Sprayable O/W Sunscreen Emulsion SPF 30 UVA

Formulation approach

An oil‑in‑water sunscreen emulsion (sprayable texture) was developed and supplemented with 3% of various eco-friendly film formers, including:

  • Polyglyceryl‑3 stearate/sebacate crosspolymer
  • Hydrogenated castor oil/sebacic acid copolymer
  • Capryloyl glycerin/sebacic acid copolymer
  • Diisostearoyl polyglyceryl‑3 dimer dilinoleate
  • bis‑Octyldodecyl dimer dilinoleate/propanediol copolymer

Most formulas were homogeneous after preparation; only the system with maleated soybean oil glyceryl/octyldodecanol esters required higher emulsifier levels to avoid phase separation.

In vitro polymer screening

  • A small amount of each formula (0.03 g) was applied to PMMA plates, dried, immersed in water at 25 °C for 40 min, dried again and visually assessed before/after immersion.
  • Best-performing polymers for homogeneity and apparent water resistance were:
    • Hydrogenated castor oil/sebacic acid copolymer
    • Capryloyl glycerin/sebacic acid copolymer
    • Polyglyceryl‑3 stearate/sebacate crosspolymer

In vivo water-resistance (ISO 16217 & 18861)

Two film-former blends were then tested in vivo in three volunteers:

  1. Hydrogenated castor oil/sebacic acid copolymer 3% + capryloyl glycerin/sebacic acid copolymer 2%
  2. Hydrogenated castor oil/sebacic acid copolymer 3% + capryloyl glycerin/sebacic acid copolymer 2% + polyglyceryl‑3 stearate/sebacate crosspolymer 1%
    1. Blend 1: Water resistance 48.3%.
    2. Blend 2: Water resistance 58%, passing the ISO water-resistance requirement.

Attempts to increase main oils (dibutyl adipate, C12–15 alkyl benzoate) and synthetic beeswax to enhance lipophilicity did not significantly improve water resistance and produced a greasier sensorial profile.

Key finding – O/W emulsion

  • Acrylate‑free combinations are needed to achieve ISO‑level water resistance in sprayable O/W systems.
  • The successful combination (Blend 2) relied on 3% hydrogenated castor oil/sebacic acid copolymer + 2% capryloyl glycerin/sebacic acid copolymer + 1% polyglyceryl‑3 stearate/sebacate crosspolymer.

4. Case Study 2 – Sunscreen Oil SPF 20

Formulation approach

A water-resistant SPF 20 sunscreen oil was formulated originally using VP/hexadecene copolymer as film former, then several eco-friendly polymers were tested as alternatives at supplier-recommended use levels:

  • Capryloyl glycerin/sebacic acid copolymer 4%
  • bis‑Octyldodecyl dimer dilinoleate/propanediol copolymer 2%
  • Diisostearoyl polyglyceryl‑3 dimer dilinoleate + caprylic/capric triglyceride 3%
  • Hydrogenated castor oil/sebacic acid copolymer 2%
  • Trimethylpentanediol/adipic acid/glycerin crosspolymer 2%
  • Maleated soybean oil glyceryl/octyldodecanol esters 3%

Most solutions remained clear; hydrogenated castor oil/sebacic acid copolymer produced a slightly opalescent oil.

Preliminary assessments

  • PMMA-plate tests did not show clear differentiation (all combinations appeared highly water resistant).
  • Therefore, in vivo UVA imaging on three volunteers’ forearms (Wood’s lamp before/after a 5‑min bath at 25 °C) was used.
  • Best performers (versus VP/hexadecene copolymer 4%) were:
    • Hydrogenated castor oil/sebacic acid copolymer
    • Diisostearoyl polyglyceryl‑3 dimer dilinoleate + caprylic/capric triglyceride
    • Maleated soybean oil glyceryl/octyldodecanol esters

Hydrogenated castor oil/sebacic acid copolymer showed behaviour most comparable to VP/hexadecene copolymer in forming a uniform film before and after water exposure.
In vivo water-resistance (ISO 16217 & 18861)

Three polymer combinations were then evaluated on three volunteers:

  1. Diisostearoyl polyglyceryl‑3 dimer dilinoleate 3% + hydrogenated castor oil/sebacic acid copolymer 2%
  2. Diisostearoyl polyglyceryl‑3 dimer dilinoleate 3% + maleated soybean oil glyceryl/octyldodecanol esters 3%
  3. Maleated soybean oil glyceryl/octyldodecanol esters 2% + hydrogenated castor oil/sebacic acid copolymer 1%
    1. Blend 1: Slightly opalescent, water resistance 60.7% (best performance; passed test).
    2. Blend 2: Clear, water resistance 47.3% (near minimum acceptable value).
    3. Blend 3: Slightly opalescent, did not pass the water-resistance test.

Key finding – Sunscreen oil

  • Complete substitution of VP/hexadecene copolymer is challenging; performance parity was not fully achieved.
  • The most promising eco-friendly option was Blend 1: 3% diisostearoyl polyglyceryl‑3 dimer dilinoleate + 2% hydrogenated castor oil/sebacic acid copolymer, which provided 60.7% water resistance while maintaining a light sensorial profile.

5. Overall Conclusions

  • Climate-responsive sunscreens must combine robust, broad-spectrum protection and water resistance with environmentally considerate choices in UV filters, film formers and packaging.
  • The studies demonstrate that renewable, bio-based polymers, particularly sebacic-acid–based copolymers and polyglyceryl esters, can provide viable, acrylate‑free film-forming systems when used in carefully optimised polymer blends.
  • Such systems support the transition to more sustainable sun care without compromising regulatory water-resistance benchmarks (ISO 16217:2020 and ISO 18861:2020).

Entity & Keyword Index

Category Items
Film formers Hydrogenated castor oil/sebacic acid copolymer; Capryloyl glycerin/sebacic acid copolymer; Polyglyceryl‑3 stearate/sebacate crosspolymer; Diisostearoyl polyglyceryl‑3 dimer dilinoleate; VP/hexadecene copolymer; Maleated soybean oil glyceryl/octyldodecanol esters; bis‑Octyldodecyl dimer dilinoleate/propanediol copolymer; Trimethylpentanediol/adipic acid/glycerin crosspolymer
Bio-actives Cyanobacteria (scytonemin, MAAs), Propolis, Usnic acid (lichen)
Concepts Climate-responsive beauty, Ocean-friendly UV filters, Eco-friendly water resistance, ISO 16217, ISO 18861, Sebacic acid chemistry

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Based on original reporting by Miriam Deola, Nicola Lionetti and Francesca Zaros from Labanalysis Life Science.