When I was learning to fly fish, I was taught to keep sunscreen, insect repellent and other contaminants off my fly.
The theory goes because trout have such an excellent sense of smell they can be discouraged by even the smallest hint of chemicals. Some people even believe sunscreens’ ability to reflect UV is visible to the trout which can also put them off visually.
I have personally followed the above advice for my entire fishing career. I consider it a fact and see no reason not to practice it.
I am not alone, for example, this quote from Strategies for Stillwater by Dave Huges
The smell of sunscreen is frightening to fish. Although it’s necessary gear, keep it off your fingers, your flies, and your leader. It can reduce your odds to nearly zero, and you’ll always blame it on something else.Strategies For Stillwater by Dave Huges
But is it actually true? Are trout even smart enough to recognize sunscreen or insect repellent as a threat? How would a trout even know that sunscreen means danger?
What does the science say?
I decided to do some research and try to give a more authoritative answer. If short on time, the answer is very inconclusive. We simply do not know if sunscreen and insect repellent can negatively affect fishing.
When trying to find answers to superstitions and beliefs regarding trout fishing, I nearly always check the scientific literature first. It certainly gives a clearer answer than anecdotal experiences from anglers that are always strongly opinion base and probably full of confirmation bias.
Will, I did quite a few searches of various scientific journals, and I found no research directly targeting this question regarding trout. The only research, which is apparently unpublished is looking at how Bonefish respond.
Flylifemagazine.com reported on research done by the Bonefish & Tarpon Trust’s. Their researchers caught bonefish from various flats and then stored them in holding nets. They then fed the captive bonefish prawns, some contaminated with various different sunscreens. The Bonefish in the trail did not care about the sunscreen and ate all the prawns.
So, there is a lot of variables at play here which makes it difficult to compare directly with trout fishing. Firstly, the smell of the natural prawns might overwhelm the smell of the sunscreen. Likewise, the captive fish might of been very hungry, so could be less fussy to feed than a trout feeding naturally in a stream.
Not all sunscreens are created equal
I feel I also need to mention, that not all sunscreens are identical. They use a wide range of different active, and inactive ingredients.
So while ‘chemical A’ in one sunscreen might repel fish, ‘chemical B’ in another brand might have no effect. Check the label, there can be a whole list of different chemicals in sunscreen so it is very hard to know which ones could potentially be affecting bites.
I personally, always try to wear sunscreen based on Zinc oxide or Titanium dioxide. The main reason, they offer physical protection against UV, rather than providing chemical protection.
Another advantage, is both are very water soluble. So they likely wash off my hands very quickly. Probably not the best for swimming, but they work well when fly fishing.
Let’s think logically for a moment.
Trout happily eat plastic lures, that stink of plastic. They will smash a fly, despite a big blob of epoxy protecting the thread.
I store my flies in a plastic fly box, which smells of plastic. Some of that scent must transfer over.
The flies and lures we regularly fish with are made with all sorts of synthetic material, and I have not once heard a fisherman say. That the trout are put off by the smell of epoxy, or the strong smell of plastic of many lures.
The more I think about it. The more I start to think this is more urban legend than fact.
But, Why take the risk, keep chemicals off our bites
Physical protection is the best protection.
I cover up with a wide brim hat, long sleeves, and pants as much as possible. But, I consider sunscreen and insect repellents are still essential items when trout fishing. If I am going to be out on the water all day, I will reapply sunscreen several times. It does lose effectiveness.
When applying my sunscreen, I always rub it on with the back of my hand. This keeps the majority of it off my palm and fingers, which in turn will keep it off my flies.
This technique is not perfect, and I probably do get some on my fingers. So I always rub my hands gently in the soil/sand, before rinsing them clean in the water. It is my belief that the combination of soil and river water should be enough to hide or wash away the majority of the chemical smell.
Sunscreen does cause other problems.
While it might be inconclusive, wither sunscreen deters` trout from biting. It does have some other negative effects.
There is evidence that contact with sunscreens can damage a fish’s protective slime layer. With the slime layer damaged, it can greatly increase the risk of bacterial and fungal infection. So, it is important not to hold fish with palms covered in sunscreen. The safest way to handle a fish is with clean, wet, bare hands.
Sun sunscreen and insect repellent can damage tackle and stain clothing and upholstery. DEET-based insect repellents in particular can melt plastic, and that is exactly what our line is made out of. I also believe DEET is quite toxic to aquatic life. So best to keep it out of the water. This is another reason why I always rub my hands in sand, before rinsing them clean.
While not directly relevant to trout fishing, some sunscreen chemicals can also damage coral reefs. So keeping them out of the water is certainly a good thing.
Finally, dissolved micro particles from sunscreen, including physical ones like Zinc Oxide can damage the gills of fish.
It is inconclusive whether sunscreen, insect repellent, and other chemicals discourage trout from biting.
This could be a case, of some sunscreen that might discourage some trout, some of the time especially if they live in heavily pressured water where the trout are educated about the danger presented to them by anglers.
While sunscreen may not definitively discourage trout will feed, it is still best practice to keep such chemicals off our hands, because they can damage our tackle and can be harmful to fish and other aquatic life.