Don&#x27;t overthink it.  Clear young skin, a near-universally accepted standard for beauty is rooted in nature.  Young fertile women have clearer skin.  So that&#x27;s the goal.  To get there women want to ether cover over blemishes (the painted woman image of the op) or basically peal off a layer of skin to expose the more youthful skin underneath (the &quot;natural&quot; look popular today).<p>a) Anything that peals of skin chemically, rather then abrasively, is going to be toxic.  The high PH of the ammonia dissolves fats and oils ... ie living tissue.  Google &quot;chemical peel&quot; for today&#x27;s version.  But dissolving skin is a very localized injury without long term side effects.  You can wreck your face, but ammonia isn&#x27;t going to give you cancer.<p>b) The painting-over approach requires something that can sit on the skin for a period of time without either dripping or being absorbed into the skin.  You need something that can block light when spread in a very thin layer.  And it needs to be shelf-stable.  So you are looking for metal  compounds, the heavier the better.  If you want white, that&#x27;s lead or zinc oxide.  Lead is cheaper.   Its toxicity, its general eagerness to play havoc with all biological reactions, keeps it from rotting away in the jar.  So the usefulness is directly tied to it being a toxic heavy metal.