Dihydroxyacetone (DHA) is the active ingredient in most sunless tanning products. It works by interacting with the amino acids in the outermost layer of the skin, called the stratum corneum. Here's how the process works:

Application: When you apply a sunless tanning product containing DHA to your skin, the DHA penetrates the stratum corneum, which is composed of dead skin cells. It does not penetrate beyond this layer, which is why sunless tans are temporary and gradually fade as the dead skin cells slough off.

Reaction with Amino Acids: Once DHA comes into contact with the amino acids in the stratum corneum, a chemical reaction known as the Maillard reaction occurs. This reaction leads to the formation of melanoidins, which are brown pigments responsible for the appearance of the tan.

Development of Color: Over the course of a few hours, the melanoidins continue to develop, resulting in the gradual darkening of the skin. This is why most sunless tanning products instruct users to wait several hours before showering or bathing to allow the color to fully develop.

Temporary Effect: It's important to note that the tan achieved through DHA is temporary because it only affects the outermost layer of dead skin cells. As the skin naturally sheds these cells through the process of exfoliation, the tan fades gradually over several days.

Erythrulose is another common ingredient found in sunless tanning products, often used in combination with dihydroxyacetone (DHA). Similar to DHA, erythrulose interacts with the amino acids in the outer layer of the skin to produce a temporary tan. Here's how it works:

Application: Like DHA, erythrulose is applied topically to the skin as part of sunless tanning products such as lotions, sprays, or mousses.

Penetration: Once applied, erythrulose penetrates the outer layer of the skin, known as the stratum corneum. This layer consists of dead skin cells that are ready to shed, and it is where the sunless tanning reaction occurs.

Reaction with Amino Acids: Erythrulose reacts with the amino acids found in the stratum corneum, similar to DHA. This chemical reaction leads to the formation of pigments that darken the skin, resulting in a tan appearance.

Color Development: The color produced by erythrulose develops gradually over several hours to a day, similar to DHA. During this time, the melanoidins formed from the reaction continue to develop, resulting in a deeper and more natural-looking tan.

Complementary Effect: Erythrulose is often used in combination with DHA in sunless tanning products. While DHA provides an initial tan, erythrulose produces a more subtle and longer-lasting color. Together, they can create a more even, natural-looking tan that lasts for several days.

Longevity: Erythrulose tends to produce a tan that lasts longer than DHA alone. This is because the reaction between erythrulose and amino acids occurs more slowly and continues to develop over time, resulting in a tan that fades more gradually.