chapter  19
28 Pages

SPF Modulation: Optimizing the Efficacy of Sunscreens

Outline 386

Introduction 386

Fundamental Requirements 387

Rheology 388

Emulsion Rheology 389

De-Emulsification Behavior 391

Formulating with Organic Sunscreens 391

Oil-Soluble Organic UV Filters 392

Effect of Emulsion Type 392

Effect of Added Emollients 393

Water-Soluble Organic UV Filters 394

Effect of Emulsion Type 394

Effect of Emulsifiers 394

Formulating with Inorganic Sunscreens 394

Basic Principles 394

Formulating with Water-Dispersed TiO2 401

Formulating with Oil-Dispersed TiO2 403

Formulating with Zinc Oxide 404

Combining Sunscreens 404

Combining Organic Sunscreens 405

Combining Inorganic Sunscreens 406

Combining Organic and Inorganic Sunscreens 406

SPF Modulation by External Factors: Water Resistance 406

Fundamental Requirements for Water Resistance 407

Strategies for Water Resistance 408

W/O Emulsions 408 Silicones 408

Specialized Emulsifiers 408

Liquid Crystal Gel Networks 409

Film-Forming Polymers 409

The “Dual-Strategy” Approach 409

Summary 409

References 410


Formulators of modern sunscreen products are required to meet ever-increasing

demands in terms of product efficacy, both for SPF claims and for broad-spectrum

(UV-A) protection. While it is well known (and intuitively understood) that SPF is

dependent on the type and concentration of UV filters incorporated in a formu-

lation, what is sometimes overlooked is the vital role played by the formulation

itself. This chapter discusses the influence of various aspects of the formulation

on product efficacy, and aims to provide the formulator with the some guiding

principles to optimize the effectiveness of UV filters in finished products.