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DHA does not penetrate living skin cells, does not interact with melanocytes, and does not affect actualy melanin production.

There's a "safety controversy" that largely stems from misinterpreted studies:

Once concern is that DHA can generate unstable molecules that can damage cells (free radicals) when exposed to sunlight. This only happens in the outermost layer of dead skin cells and wearing SPF on top takes care of it.

The DNA damage claim comes from lab studies that doused living skin cells in much higher concentrations of DHA than you'd ever find in a self-tanner. That's not really a meaningful comparison to putting self-tanning lotion on your skin.

Regulatory bodies around the world, including the EU's Scientific Committee on Consumer Safety (SCCS) and the U.S. FDA consider it safe for use in cosmetics when applied topically (maximum 10%, and most self-tanners contain between 3-5%).

Ethoxydiglycol also helps deliver other key ingredients into the skin.

Industry-reported use ranges from 8% in rinse-off products and 2% in leave-on formulations.

Your skin makes glycerin on its own (mostly from sebaceous oil breakdown) and shuttles it to your outermost layer of skin, or your epidermis, via aquaporin-3.

Aquaporin-3 is a transporter that is essential for normal skin hydration, elasticity, and repair. Interestingly, mice lacking in AQP3 have dry and less elastic skin that can be fully corrected with glycerin.

This ingredient is non-irritating, plays well with almost every ingredient, and works across all skin types. Typical use is anywhere between 3-10% but can go up to 79% in some leave-on products.

Just know very high concentrations (>40%) can feel tacky in low humidity.

Glycerin is the name for this ingredient in American English. British English uses Glycerol/Glycerine.

D-panthenol is also known as dexpanthenol. Most cosmetics use dexpanthenol or a mixture of D and L-panthenol.

Panthenol is famous due to its ability to go deeper into the skin's layers. Using this ingredient has numerous pros (and no cons):

Like hyaluronic acid, panthenol is a humectant. Humectants are able to bind and hold large amounts of water to keep skin hydrated.

This ingredient works well for wound healing. It works by increasing tissue in the wound and helps close open wounds.

Once oxidized, panthenol converts to pantothenic acid. Panthothenic acid is found in all living cells.

This ingredient is also referred to as pro-vitamin B5.

The CIR Expert Panel has confirmed this ingredient to be nontoxic and clinical studies show no sensitization at cosmetic use concentrations.

True allergic reactions are quite rare: a 15-year retrospective study of 6,751 patients found only 0.31% had a positive reaction (and less than half were considered clinically relevant).

It seemed that when sensitization does occur, it's most commonly linked to topical medication (like corticosteroids) and not cosmetics. Allergic contact dermatitis also appears largely limited to individuals with underlying skin conditions.

Overall, propylene glycol is a well-studied ingredient that most people can tolerate without issue.

You'll also recognize water as that liquid we all need to stay alive. If you see this, drink a glass of water. Remember to stay hydrated!