Is HPR(Hydroxypinacolone Retinoate) Retinol really mild and not irritating?

Retinoids are substances that are similar in structure and function to retinol, including:

Drugs such as retinoic acid (RA), isotretinoin, adapalene, tazarotene, etc.;

Retinol (retinol), retinaldehyde, retinyl palmitate, retinyl propionate, retinyl retinoate, and now the up-and-coming hydroxypinazone retinoate (HPR), among others.

These substances can be converted into each other, so that there is a transformation pathway:

After the body absorbs retinol, if it can't consume it, it converts it into retinyl palmitate and stores it, and when needed, hydrolyzes the palmitate bond with esterase (the red position in the retinol ester structure diagram on the right is broken), and retinol is released.Retinol is stripped of a hydrogen atom and oxidized to become retinaldehyde, which is an intermediate state.

Retinaldehyde is further oxidized, adding an oxygen atom that becomes retinoic acid.Retinoic acid (tretinoin/retinoid) is the actual form of retinoid that enters the nucleus to bind to trans-retinoin reaction elements (RAR/RXR) and initiates the corresponding gene expression.

It not only retains the efficacy group of tretinoin, but can directly bind to the receptor; It also covers the irritating groups and improves the physical and chemical stability.

Cosmetics containing HPR (Hydroxypinacolone Retinoate)  can be used even on VA-sensitive skin, but note that pregnant women should not use them!