Lactic acid can be summed up in one visual:
That's in the simplest of terms - of course, but if you want a gentle acid that most skins can get on with, that gently exfoliates the surface of the skin, doesn't penetrate too deeply and cause deeper irritation and redness, try lactic, aka the Pac Man of acid.
Traditionally derived from milk, a lot of lactic acid in skincare these days is actually synthetically derived, making it safe for people who had previously avoided it because they were worried about allergies/veganism etc.. 
As one of the core AHAs (alpha-hydroxy acids), lactic is readily available in a lot of products although my personal preference is to use it at the toner/post-toner stage. Easy to use, it stays on the skin and you can follow with your usual routine. I don't tend to use acids in cleansers as I am so used to rubbing them into my eyes that you just know I would be the person that does themselves a serious injury.
You can expect lactic to gently exfoliate, smooth out lines, help fade pigmentation (help, not eradicate) and stimulate cell turnover. One added bonus is that it does this without further drying out your skin. It works brilliantly with a good mist over the top, followed by your serum/moisturiser/spf etc.
It's safe for all ages, skin types, people and conditions including pregnant, breastfeeding and darker skin tones. Obviously, if you have psoriasis, eczema or broken skin for some other reason, don't be putting acid on it please.
Some excellent products including lactic acid are:
Summer Fridays Soft Reset AHA Exfoliating Solution: https://bit.ly/3b0DD7K
Pestle & Mortar NMF Lactic Toner: https://bit.ly/36LaLjG
Tarte Knockout Tingling Treatment: https://bit.ly/30Mkfr5
Dr Dennis Gross Gentle Alpha Beta Peel Pads: https://bit.ly/3bthRbN
OSKIA Liquid Mask Lactic Acid Micro-Peel: https://bit.ly/39qfzuH
The Ordinary Lactic Acid 10% + 2% HA: https://bit.ly/3q8IslD
Allies of Skin Bright Future Overnight Facial: https://bit.ly/3bxrucG
Kate Somerville ExfoliKate Glow Moisturiser: https://bit.ly/3qbfSAd
Paula's Choice AHA Treatment: https://bit.ly/3numKqE
The Inkey ListLactic Acid Serum: https://bit.ly/3bvaP9y
Renee Rouleau Triple Berry Smoothing Peel: https://bit.ly/2MM5aBK
Joanna Vargas Exfoliating Mask: https://bit.ly/2Xz0FfS
Deviant Skincare Gentle Resurfacing Liquid: http://bit.ly/3nvtwfH
