Yes, titanium dioxide and zinc oxide is in some minerals

…and those are two of the most common active ingredients in sunscreen. If the sunscreen bottle says “PABA free”, it’s typically because it’s based on one of these two minerals instead.

While there are sunscreens not based on any of these three active ingredients, the book doesn’t give the formulation of her sunscreen, so to say her sunscreen contains any particular one of these is to make an unfounded leap of logic.

Regardless, what is your solution? Should Kaitlyn do no magic at all at this point in the book? How long must a mage wait after wearing sunscreen to do magic?

Or should Davie let her cook instead? Sure, Davie could heal her afterward, but I don’t want that talent revealed any earlier in the book than I already have it. Which is Chapter 24, by the way!

it has been banned in sunscreen in Europe

Largely on allergy grounds, and then only to something like ~8% of people. None of that has anything to do with magic.

…Or would you say that a poison ivy case would also cause a mage to lose the ability to do magic?

In any case, “Europe banned it” is a weak argument. They also banned leaded solders in electronics without any evidence it was getting into the water supply, with the unintended consequence that there is now more e-waste because electronics made with unleaded solders tend to fail more easily.

That ban went into place through a mixture of moral panic and false analogy.

Lead-free plumbing solder is a good idea, because that’s directly in contact with drinking water.

The prior ban on lead flashing on housing also makes sense, since rain washes some of that into the gutters and thence into the water supply.

Unleaded gasoline was also a good call: people breathe that stuff!

But e-waste? If any of that lead is getting into the water supply, the problem is in waste handling, not in the electronics industry using leaded solders.

even if all chemicals in a sunscreen do occur natural somewhere, the mixture of them in sunscreen doesn’t.

If I prevented my mages from coming into contact with every “unnatural” combination of ingredients, there is no story.

Book 2 begins with Kaitlyn making a salad. Where in nature do you get the salad dressing pod to squeeze over the vegetables? Doesn’t that make it an unnatural combination of ingredients, just like sunscreen? Vegetable oil has to be boiled out of things, vinegar has to be produced in casks, herbs have to be grown, diced, and dried… Almost everything is technology if you chase if far enough.

It isn’t explicitly stated in the early chapters of Book 2, but presumably Kaitlyn and Davie eat the salad. How long are they prevented from doing magic, until all of that technological salad dressing is fully flushed from their bodies?

a gravel road stopped Kaitlyn from being invisible

It wouldn’t have stopped Davie, as we see from Chapter 1. Kaitlyn’s a newbie at that point, so she can’t quite handle the interference yet.

Anyway, you’re comparing tons of gravel and tire dust under her feet to a 25 micron layer of sunscreen — I did the math! — over her body. Even if you multiply that thickness by the fraction of foot sole area to whole-body area, I think there’s more influence of the roadbed on Kaitlyn’s body than that of the sunscreen, even had she been freshly-coated at the time.

…Which she was not, as you may recall, because Davie told her not to put sunscreen on that morning!

All of this aside, you will find that the mages use less sunscreen as the book proceeds. Book 3 doesn’t use the word at all, Book 4 uses it only in relation to non-mages, and Book 5 doesn’t use it yet, though it may eventually do.

I have now read chapter 23 and I still don’t grok why sunscreen is natural in the context of the story. Yes, titanium dioxide and zinc oxide is in some minerals (alhough zinc oxide never is natural in pure form – natural occurances of zincite always also contains some mangan and/or iron). PABA indeed ̣occurs extensively, also in humans, but it has been banned in sunscreen in Europe where I live for years. Several other organic ingredients in sunscreen don’t occur natural. But even if all chemicals in a sunscreen do occur natural somewhere, the mixture of them in sunscreen doesn’t, and sunscreen absolutely is technology.

I chapter 22 a gravel road stopped Kaitlyn from being invisible because the road wasn’t natural. Yet a gravel road doesn’t contain anything not found in nature. So if the road isn’t natural, why is sunscreen?

You’re kind of jumping the gun here, Jensen. The novel touches on this matter later, in Chapter 23. This is a common technique in fiction, where we purposefully don’t open the kimono fully the first time a topic comes up. Sometimes it’s done to build dramatic tension, but here I just didn’t want to perform a complete technical brain-dump about sunscreen in the middle of a fantasy story.

However, that chapter directly contradicts your claim about naturalness, partially in support of one of the novel’s major themes, which is, “What is ‘natural’, really?”

If by “natural” you mean a liquid growing in a pod on a tree, which you just have to squeeze out onto your skin, then yeah, there are no natural sunscreens other than mud and ash, as still used by some primitive people, such as the African bushmen.

However, many of the elements of a modern sunscreen are naturally-derived:

* PABA “…occurs extensively in the natural world” according to Wikipedia.

* Titanium dioxide and zinc oxide can literally be found in mineral form on the ground.

etc.

As to how and whether this affects a mage’s power, observe that the material absorbs into the skin, where the body either breaks it down or sends it through the elimination system. If all such substances prevented a mage from using magic, my mages would probably have to fast for days before I could get them to do anything useful for the novel.

Therefore, in the name of literature, I claim that sunscreen doesn’t completely prevent a mage from using his or her magic. You are welcome to provide a counter-proof, of course. 😉