Why Does Sunscreen Sting Your (and your kids) Eyes?

It’s happened to all of us, a drop of sunscreen or soap rolls into your eye and suddenly there's intense burning, tearing, and that desperate urge to rub. But what's actually happening inside your eye at that moment?

Your Eye Has a Ridiculous Number of
Nerve Endings

The surface of your eye, the cornea and conjunctiva, is one of the most densely innervated tissues in the entire human body. Most of those nerves are tiny branches off the big trigeminal nerve, the same one responsible for all facial pain and sensation. When something touches your eye, these nerves sense it and fire an electrical signal to your brain. 

How does the nerve know what touched it? Each of the nerves we care about here has specialized protein channels (called TRPV1 and TRPA1) that are essentially tuned to detect specific events. These channels respond to an valmost absurd range of stimuli: heat, acid, chili peppers, and yes, your sunscreen ingredients. Critically, they don't work like an on/off switch. Think of them more like a volume knob, a little stimulus might barely register and even “feel” nice, but crank it up and your brain registers it as an emergency. So, when something really stings your eye, it means two things: your sensors are wired to recognize that “something” as unwanted, and there's enough of it that your nervous system has decided your brain needs to know. Now.

What Your Eye Does Next

That sting triggers an immediate, coordinated response:

• Reflex tearing floods the eye to dilute and flush out the unwanted stuff

• Blinking physically sweeps the tear film across the surface

• Blood vessel dilate (get big) causing redness as immune cells rush to the area

• Mast cell activation can release histamine if your immune system recognizes the chemical as an allergen - adding an itching component on top of the sting, which is its own special kind of miserable

And repeated exposure to an irritant can actually make you more sensitive to that irritant.  What starts as mild stinging after heavy sweating can, over time, become stinging from minimal exposure. 

Part of the reason is how sensitization works.  Things that sting can cause problems two ways. Some are directly irritating, they activate those nerve receptors we just talked about on contact, or at high enough concentrations they can damage cells outright. Others are not directly harmful but your immune system simply doesn't like them for whatever reason, and it's the immune response itself that's unpleasant, not the substance doing direct harm. Pollen is the perfect example: it's not toxic, but for millions of people the immune system treats it like a threat, and the reaction is miserable. Some ingredients are both: directly irritating at the surface and capable of training your immune system to overreact to them over time. Some fragrance molecules fall into that category, which is why fragrance sensitivity tends to get worse with repeated exposure rather than better.

Why Sunscreens Specifically

A lot of things burn when they get in your eyes, natural or not. That makes sense. Your eyes are delicate and your body is deeply committed to keeping stuff out of them, so the alarm system has a hair trigger.

But what is it specifically about sunscreens? Individual chemistry varies: what scorches your eyes might not bother someone else, but certain ingredients are known to cause more problems than others:

• Some UV filter chemicals - certain chemical sunscreen agents like avobenzone and octocrylene are commonly associated with stinging, though even here the data is thin. There have been limited studies, and the problem is so widespread it's barely tracked.

• Some preservatives - particularly older preservative systems 

• pH mismatch - your eye operates at a very specific chemistry. Products that are too acidic or too alkaline trigger stinging the moment they hit the surface.

• Fast-evaporating ingredients like alcohol - as they flash off, they concentrate other irritants on the surface, and many are direct irritants themselves

• Salt concentration - your eye is surprisingly particular about how much dissolved material is in the liquid touching it. Too much or too little and it stings immediately. This is the same reason pool water can burn your eyes while the ocean mostly doesn't.

• Some fragrances are among the better-studied irritants

• Some emulsifiers - these are the molecules that make sunscreen lotion possible, keeping the water and oil parts from separating into a useless mess. There are many types, but the emulsifiers used in traditional lotions are significantly more likely to be irritating than those used in reverse emulsions. More on that in a second.

The Best Solution

We could avoid every ingredient that might irritate eyes, but some of those ingredients are genuinely useful (just not in your eye.) Pepper is a terrible eye experience and an essential food and source for medicines. Context always matters.

burnd's approach here shares a lot with our philosophy on reef safety: the best way to keep ingredients from stinging your eyes is to keep them out of your eyes entirely. Duh.  But most sunscreens aren't actually built with that goal in mind.

Our reverse emulsion technology makes burnd formulas far less likely to dissolve in sweat, or the ocean, which means far less likely to migrate into your eyes in the first place. On top of that, the emulsifiers we use are inherently non-irritating, and we work hard to keep the rest of the formula gentle.

If you want a product that actually performs and was purpose-built by people who understand the chemistry, physics and biology behind what they're making. That's what we do here. We love our marketing gnomes and couldn't survive without the accountants, but Product is the number one thing at burnd. Period.