The sunscreen market is a growing one and to be a competent cosmetic chemist, you should know the basics of how to formulate one.
How a sunscreens work
A sunscreen is typically a skin lotion with added UV blockers or absorbers. UV exposure from the sun has a number of negative impacts on skin such as burning, wrinkle causing and cancer. So, sunscreens are designed to protect from these. There are two ways in which they can work. First, they have ingredients that block or reflect sunlight. Second, they have compounds that absorb sunlight and convert it to a less harmful energy like heat. These sunscreens are oil-soluble or disperseable so emulsions are excellent delivery vehicles. Sunscreens are also available in gel and aerosol forms but we’ll save those types for another post.
When a sunscreen lotion is put on the skin, it forms a continuous film which provides protection from UV rays. Ideally, this film will spread easily and will be resistant to wash-off.
In the United States, sunscreens are classified as OTC drugs and are regulated by the FDA. Accordingly, there are a limited number of approved sunscreen active ingredients. You can find a complete list of approved sunscreens in the FDA sunscreen monograph. For our purposes, we’ll just mention a few of the more common actives; Titanium Dioxide, Zinc Oxide, Avobenzone, Benzophenone 8, Octocrylene, and Oxybenzone. To vary the amount of sun protection, the level of the active ingredient is adjusted.
The most common moisturizing ingredients are occlusive agents which create a barrier that blocks water from escaping the skin. Ingredients like Petrolatum, Mineral Oil and Dimethicone can all be used as occlusive agents. Humectants, which are ingredients that attract water, are also added to lotions. Glycerin is the most commonly used humectant. Finally, emollients are added to improve the feel of the lotion on the skin. They can reduce the tackiness and greasiness caused by the other moisturizing ingredients. Common emollients include coconut oil, cetyl esters, and certain silicones. Sunscreen formulations are typically thinner in viscosity than standard skin lotions.
In addition to the moisturizers, sunscreens contain emulsifiers to make the oil and water compatible. There are suspending agents, neutralizing agents and thickeners. Finally, to make it a complete and stable formula raw materials such as fragrance, preservative, and colorants are also included.
Here is a typical sunscreen formula.
Click on image to enlarge it.