# How to Make Clear, Waterproof Sunscreen That Doesn't Feel Greasy

> A 1989 patent for a transparent, water-resistant sunscreen formula that uses wood rosin to create a non-sticky, long-lasting protective film on the skin.

- **Patent:** US 4810490
- **Original title:** Sunscreen composition
- **Owner:** Carter Wallace Inc
- **Granted:** 1989
- **Status:** Public domain (expired)
- **Times cited:** 11
- **Field:** consumer_electronics, materials

## What it does

This patent describes a specific chemical recipe for a sunscreen that remains clear and resists washing off in water. The core of the invention is the use of the methyl ester of hydrogenated wood rosin, which acts as a film-forming agent. By mixing this resin with specific solvents like ethanol or mineral oil, emollients like volatile silicone, and UV-absorbing chemicals, the formula creates a thin, durable layer on the skin. This layer stays on even when the wearer is swimming or sweating, while avoiding the heavy, oily feeling common in older sunscreen products.

## What it does NOT cover

- Does not cover sunscreen formulas that lack the methyl ester of hydrogenated wood rosin.
- Does not cover physical sunscreens that use mineral ingredients like zinc oxide or titanium dioxide.
- Does not cover non-clear or opaque sunscreen lotions or creams.
- Does not cover spray-on delivery mechanisms or aerosolized sunscreen delivery systems.

## The clever bit

The inventors discovered that using the methyl ester of hydrogenated wood rosin creates a film that is both water-resistant and non-tacky, solving the classic trade-off between durability and comfort.

## Real-world examples

1. Clear sunscreen gels
2. Water-resistant sunscreen oils
3. Sport-formula sunscreen liquids

## Why it matters

Before this invention, many sunscreens were thick, white, and greasy, which discouraged frequent use. This patent helped shift the industry toward 'elegant' formulations that were pleasant to wear, which is critical for public health compliance in sun protection. It represents a transition period where cosmetic chemistry began focusing as much on skin feel as on UV protection.

## Frequently asked questions

### What does How to Make Clear, Waterproof Sunscreen That Doesn't Feel Greasy cover?

A 1989 patent for a transparent, water-resistant sunscreen formula that uses wood rosin to create a non-sticky, long-lasting protective film on the skin.

### Who owns patent US 4810490?

Carter Wallace Inc owns this patent, granted in 1989.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 4810490 cited by?

This patent has been cited by 11 later patents that build on its ideas.

### What problem does this patent solve?

Before this invention, many sunscreens were thick, white, and greasy, which discouraged frequent use. This patent helped shift the industry toward 'elegant' formulations that were pleasant to wear, which is critical for public health compliance in sun protection. It represents a transition period where cosmetic chemistry began focusing as much on skin feel as on UV protection.

### What does this patent NOT cover?

Does not cover sunscreen formulas that lack the methyl ester of hydrogenated wood rosin.

**Full plain-English explainer:** https://patentbrief.org/patent/us/4810490/tpa-tissue-plasminogen-activator

**Original patent:** https://patents.google.com/patent/US4810490

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._