Wrinkle-removing and exfoliating ingredients, fat-soluble vitamin A acids are extremely sensitive to light, and when the concentration is too high (above 0.5%), they are easy to irritate the skin, and should not be used together with whitening ingredients as much as possible (prone to irritation)[1].
As far as the same concentration is concerned, the effect and irritation are Retinaldehyde>Retinol>>>Retinyl Linoleate, but the opposite is true in terms of mildness and stability[2].
[2] 邱品齊，「認識你所不知道的藥妝品：皮膚科醫師特選篇」，大境，2010/03/18。
曾經用過維A酸軟膏祛斑 小小嚸搽有刺痛感 當你多一點嚸劑量 就會印發過敏 紅斑紅點 三日才康復
Why 安心度 is 9?
why 9?
EWG rates it as 8 (out of 10), with overall hazard level rated as ‘high’. They also claim it’s a known to cause birth defects and accelerate development of skin cancer.
All of which are true, sort of. But here again we see that they string together factoids out of context to spin their narrative.
It’s true that overdose of oral vitamin A can cause birth defects and other problems. That’s why derms are careful when prescribing Accutane, and that’s why women taking Accutane must use birth control.
This is not applicable to retinol used in acne and personal care products. Studies have shown that the vast majority, if not all, of topically applied retinol is metabolized in the skin, i.e. it never makes it to the bloodstream and thus cannot cause birth defects.
http://www.acneeinstein.com/chemical-myths/
“Retinol”维生素A醇，也称视黄醇。脂溶性维生素A酸类物质。A酸的主要作用是对抗痤疮和衰老。比较刺激，效果迅猛，但副作用也大，主要表现在：角质层变薄，发红蜕皮，干燥，可能导致胎儿畸形，所以在护肤品中不允许使用。于是各大品牌就打起了A酸衍生物的主意。A醇就属于A酸衍生物。由于不是直接的A酸，并且还有一个转换率的问题，A醇要先转换为A醛，然后再转换A酸发挥作用，所以比A酸要温和很多，特别适合日常保养。
视黄醇能够指令皮肤细胞正常工作，甚至创造更好，更健康的皮肤细胞，让皮肤变得更加富有活力；同时增加皮肤的胶原蛋白生产和糖胺聚糖含量，改善肤质，更坚固皮肤的屏障功能。
注意：1. 视黄醇对光线极为敏感，所以大部分产品只能夜间使用，白天使用一定要注意防晒！并且应尽量避免与美白成分共同使用(容易产生刺激)。2. 孕妇请远离含有这类成分的产品。
能和抗坏血酸叠加吗
Tham khảo thông tin chi tiết về thành phần làm đẹp và chăm sóc da này tại: https://hellophaidep.com/retinol-la-gi-va-cach-dung/
A醇可幫助皮膚製造比較健康的皮膚細胞，並增加支撐皮膚的物質，所以皮膚會變得比較緊實、細緻，同時提高皮膚障壁的功能
https://www.paulaschoice.com.tw/learn.php?learn=2180
为何不能与美白成分一起使用呢？网络很火烘的视黄醇+烟酰胺一起搭配使用，请问这样子行得通的吗？
我也想知道
A醇與抗壞血酸、煙酰胺等成分搭配都是可以的，沒什麼特別的禁忌，一些產品也會同時含有以上幾種成分。實在擔心，使用時可以間隔幾分鐘。不過，抗壞血酸、煙酰胺等成分本身都具有一定的刺激性，與A醇同時使用，需要考慮自己皮膚的耐受度。