Want to prevent tick-borne disease? Start by preventing tick bites.
Many people forgo easy steps to reduce risk of vector-borne illness
Since the piece I wrote earlier this week about ineffective insect repellents, I’m pleased that Museum of Science finally replied and removed the video (so if you don’t see it in that article, that’s why). Kudos to them for listening to experts on the topic and removing this harmful misinformation. I hope that in the future, they will consult legitimate experts and not feed into the rampant world of misinformation, chemophobia, and appeal to nature fallacies.
That said, Lyme pseudoscience is still rampant this time of year, and it coincides with people getting tick bites.
Recently, Dave Asprey (more on him to come, but he has zero business being considered a source of science or health information whatsoever), posted a reel where he is spreading misinformation about Lyme disease and toxic mold syndrome: both topics which are rife with false claims from wellness influencers.
I’ve tackled the realm of misinformation in both these spaces in my Skeptical Inquirer column Inside Immunity, so definitely check them out there! But it brings up a bigger topic of conversation in that we can actually do a lot to prevent the risk of any types of tick-borne diseases by preventing tick bites to begin with.
The problem is, not enough people take these proactive measures to prevent tick bites in the first place. But if you aren’t bitten by a tick (including a tick that is the right species and carrying a potential-disease causing pathogen), then you aren’t at risk of getting any sort of disease.
Remember the difference between a hazard and a risk? Hazard: tick-borne disease. But there’s no risk if you’re not bitten by a tick in the right environment.
That brings us to the epidemiological triad: the conditions in which a disease can actually occur.
In the case of tick-borne diseases, it is even more complex than this, because most of the pathogens need to live inside a secondary reservoir host (like a mouse, or a prairie dog, or a dog), and the pathogen has to adapt to live inside an arthropod environment with vastly different temperature and nutrient conditions, but I’m going to keep it simple for the time being. The tick-disease-human relationship is complex.
Add to that the fact that there are nearly 900 species of ticks on the planet and only a handful pose potential concerns to humans, and, you can understand why it is confusing to most people.
Ultimately you need (3) major components: you need to be in an area in which you’ll be realistically exposed to the vector - in this case, a tick, the tick must be carrying the particular pathogenic microorganism of concern, and you must actually be exposed.
What those details mean vary depending on the pathogen. For example, in the case of Lyme disease, that means:
you need to be in a geographical region where Ixodes scapularis or Ixodes pacificus ticks live (the two species that *can* transmit Lyme bacteria to humans)
the tick in question actually must have the bacteria within its midgut (remember, not all ticks are infected)
and the tick must attach to you and feed on you for a sufficient period of time to have the potential to transmit the bacteria to you.
finally, they must get into your body in sufficient numbers where they can actually establish an infection (and avoid the rapid immune responses of your innate immune system).
If you can prevent some of these conditions, you can prevent your risk of getting disease.
The first step to prevent the risk of tick-borne illnesses? Prevent tick bites.
The great news is there are many step you can take to prevent tick bites in the first place - provided you live in an area where tick species that can cause human disease live. In some places of the world, this isn’t even a legitimate concern.
Step one: effective tick repellents should be applied to the skin.
If you recall from Tuesday’s newsletter, that means not listening to people on social media recommending “natural” or alternative options, and rather, using those that have data that they work to repel ticks.
Before entering the market, most skin-applied repellents must be registered by EPA indicating that they have been evaluated and approved for human safety and effectiveness. Spoiler: citronella oil, cedar oil, geranium oil, peppermint and peppermint oil, soybean oil have NOT been evaluated for safety for humans.
DEET and picaridin are the two insect repellents with efficacy data against tick species.
Repellents do not kill ticks, but affect their sense of smell and taste. When applied, ticks cannot detect humans in their vicinity, which ultimately prevents tick bites. These two chemicals are safe and effective for anyone 2 months and older and during pregnancy. Neither kill insects/arthropods, they work by rendering their ability to detect us less effective.
DEET (N, N-diethyl-meta-toluamide) is an insect/arachnid repellent that was developed in 1946 by the U.S. Army. It has been used by the general public since 1957.
DEET has decades of safety and efficacy data. (Do NOT confuse DEET with DDT, which was an insecticide of completely different chemistry that was banned in 1972).
Picaridin/Icaridin (1-piperidinecarboxylic acid 2-(2-hydroxyethyl)-1-methylpropylester) is an insect/arachnid repellent that was developed by Bayer in the 1980s.
Picaridin was licensed for use in the US in 2001, and has been widely available here since 2005 after EPA approval. It has been used in many other countries globally for longer: Germany and most of Europe since 1998, Australia since 2000, Japan, China, India, and others in the early 2000s. Just like DEET, it also has decades of data to demonstrate safety.
DEET and picaridin both interfere with the ability of ticks to detect and sense your presence, thereby “masking” you from them and reducing their questing behavior to climb onto you. (I discussed their mechanisms of action in more detail here).
Both DEET and picaridin work by creating a vapor barrier on our skin.
When applied to the skin, these chemicals evaporate and form an invisible vapor barrier just above our skin (a layer of gas). This is how the chemicals work, which is why applying them under clothing is not going to be effective. This is also why you want to apply them as your top layer, so if you are putting sunscreen and repellent on, sunscreen goes directly onto skin first, then apply your repellent 10 minutes afterward on top.
DEET and picaridin concentrations relate to duration of protection.
This is related to the evaporation rate: once you lose the vapor barrier, the repellent is no longer effective. You can find DEET concentrations ranging from 10% to 98%. For tick prevention, 10% DEET will provide protection for about 2 hours, whereas 20-30% DEET will be effective for about 6-8 hours. (for mosquitoes, protection lasts a bit longer). Higher concentrations of DEET will last 8-10 hours, but if you sweat, that will reduce the duration of protection.
Picaridin products typically range from 20-40% concentration. 20% picaridin is effective against ticks for about 6-8 hours, similar to 30% DEET. Some people prefer picaridin over DEET because it is odorless and the texture may be preferable for individuals, but both are equally effective and safe for use for anyone 2 months and older.
For kids under 10, you’ll want to apply repellent to them, to ensure it is appropriately applied. If you’re applying to your face, first spray the product in your hands, and then rub onto your face.
What about other EPA-registered insect repellents like OLE (Oil of Lemon Eucalyptus) or IR3535 (ethyl butylacetylaminopropionate)?
These other two EPA-registered repellents have data to suggest they have some efficacy against mosquitoes.
However, their efficacy is far more variable, particularly when it comes to ticks. Even when assessing efficacy against mosquitoes, duration of protection was shorter. This means you need to reapply more frequently, or be concerned that ticks are still going to find you.
Importantly, the data available do not suggest they are sufficiently effective against ticks, particularly if you live in an area with high tick prevalence especially when compared to DEET and picaridin. I understand the perception of utilizing something “natural”, but both of these chemicals are still synthesized in a laboratory, and IR3535 is a synthetic chemical.
OLE is an essential oil mixture, derived from leaves of the lemon eucalyptus tree (Corymbia citriodora). The primary chemical that has some repellent effects is p-Menthane-3,8-diol (PMD). But like other essential oils, it is a complex mixture of dozens of chemicals, including citronellol, isopulegol, citronellal, limonene, and β-pinene.
Part of the variability in efficacy with OLE is the fact that because this is not a single chemical and it is extracted and processed from plant material means that the purity and concentration of the active ingredient (PMD) can be different depending on the product. While it is often refined further to increase the concentration of PMD, it will still vary product to product.
Many people are misled by emotional marketing to appeal to this notion that “natural is better” or safer. This is simply not true and is the epitome of the appeal to nature fallacy (which I’ve discussed here).
Essential oils, because they contain many chemicals, can be harmful to certain individuals, including young children. That’s why there are explicit warnings about not using OLE on children younger than 3 years old. Essentials oils can also be incredibly harmful for pets, if they are exposed topically, if they accidentally ingest, or if you diffuse them around your home.
In contrast, DEET and picaridin are safe for anyone 2 months and older, and during pregnancy. (Side note: kids younger than 2 months shouldn’t be in a situation where tick exposure is a legitimate concern - they won’t be walking in tall grasses or forests independently).
DEET and picaridin do not pose a risk to the environment or aquatic or terrestrial organisms.
EPA has concluded that DEET poses low risk of bioaccumulation and is unlikely to expose ecology to high concentrations. These chemicals are readily broken down in soil by microorganisms. EPA has concluded that DEET poses low risk of bioaccumulation and is unlikely to result in aquatic or terrestrial exposure to non-target organisms
Just like anything, the dose makes the poison. So while you can find claims that these repellents are “toxic” to wildlife, these are incredibly high levels. DEET concentrations that have the potential to kill fish and insects is 75,000 times greater than the highest concentration ever found in wastewater or streams.
DEET, like other topical substances, is not absorbed by the body. It can be detected in minute quantities, but even in that instance DEET is broken down rapidly by the liver and eliminated mostly through the urine, within 24 hours. There is no evidence that these chemicals cause cancer in animals or humans.
If it were me (and it is me, since I grew up adjacent to Lyme, CT, lived on Long Island, NYC, Westchester County NY, Northern NJ, and now eastern PA)?
I would not fall prey to the false perception that “naturally derived” chemicals are better and I would use only the safe and effective repellents: DEET and picaridin.
You’ll want to apply these repellents to your skin before heading out to enjoy the outdoors. Using effective repellents is an important step in preventing vector-borne diseases so that you can enjoy the outdoors with more peace of mind.
Step 2: treat clothing with permethrin, an insecticide, which kills ticks after contact.
Permethrin is an insecticide that is highly effective at killing ticks that may crawl on you, especially if you are in areas with high tick activity. Permethrin is a pyrethroid, which is a synthetically altered version of pyrethrins, chemicals produced by certain Chrysanthemum species, the Dalmatian chrysanthemum and Persian chrysanthemum. Fun fact: pyrethrins, which are also insecticides, are commonly used as organic pesticides (remember, organic is not remotely pesticide-free).
Permethrin affects sodium channels in insect and arachnid nervous systems. Normally, sodium channels open transiently and then close quickly - a process essential for normal nerve signaling. Permethrin prevents sodium channels from closing, which disrupts the cycle of nerve cells. This causes continuous nerve firing, ultimately leading to paralysis and death of the insect or arachnid.
When applied to clothing, permethrin binds tightly to the fabric when it dries, providing long-lasting protection even through several washes. Permethrin can be protective through several washings - if you purchase pre-treated clothing, this can last up to 70 washes, depending on the product. Treat clothing and gear, such as boots, pants, socks, and tents, with products containing 0.5% permethrin according to instructions.
Permethrin, like everything, has selective toxicity, meaning impacts on insects and arachnids are not the same as in mammals or other organisms. In mammals, permethrin is rapidly metabolized and excreted, due to physiological differences among organisms. However, liquid permethrin can be particularly harmful to cats, so you should never apply permethrin to materials where a cat can encounter it. Once dry though, permethrin poses no risk.
Step 3: Perform thorough tick checks - including your crevices.
Check your clothing, gear, and pets for ticks. Contrary to popular belief, ticks climb UP your body, usually after hanging from a blade of grass when they sense chemicals you excrete, a process called questing.
If a tick climbs onto you (or your pets), it takes them between 15 minutes and 2 hours to crawl up and find a suitable place to attach and feed, so being prompt about checking for any unattached ticks can reduce your risk of potential tick bites.
Full-body checks are really important, especially if you were in areas where ticks might be prevalent. This means all the protected, warm, and dark areas of your body: under the arms, the groin/genital areas, in and around the ears, inside the navel, behind the knees, between the legs, around the waist, and in the hair. Ticks are often attracted to warmer areas of the body, so make sure to check all creases and warm area folds. Since ticks can be very small, it’s important to feel for bumps on the skin that might not be immediately visible.
Children may not be as diligent about tick checks, so if you have kids, you should check them. If you were outdoors earlier in the day, you can also do a final tick check before bed, especially if you’ve been in a high-risk area.
If you have dogs that walk in the woods with you:
Pets should always be treated with ectoparasite medications (topical or oral). However, most of these require a tick to physically bite onto your pet and start feeding before the medication will kill them. So it’s also important to comb your dog well and remove and crawling ticks on them. If not, they may fall off onto furniture, carpeting, etc., and ultimately find you as their new food source (this is one of the more common ways people get bitten).
Step 4: other behavioral steps can prevent tick bites.
The number one most effective method to prevent tick bites are insect repellents on skin. Unfortunately, not enough people use those: many people use ineffective alternatives that are falsely positioned as being effective, or they forgo them altogether. That single step is going to nearly eliminate risk of tick bites.
In addition to that and the other things listed above, you can take other measures to further reduce risk.
Showering promptly after spending time in tick-infected areas: ticks like to climb around for a bit, so showering will be another effective tool to remove any crawling ticks.
Changing clothing after spending time outdoors: if a tick has crawled onto your clothing, it can take time for them to find your skin. If you continue to wear those clothes, that increases the chance they might bite you. Changing your clothing, or tumbling them in the dryer on high for 15-30 minutes can reduce that risk further.
Removing any attached ticks promptly: for most potential tick-borne infections (regardless of the specie of tick or pathogen), it takes time for the tick that is feeding on you to physically transmit the pathogen. That means, if you do prompt tick checks and find a tick attached, removal also substantially reduces the likelihood you might get infected, provided the tick was carrying an pathogen.
It is only recommended that you remove ticks mechanically using fine-tipped tweezers. Read the full instructions at the American Lyme Disease Foundation website here.
I get it: ticks are not the most attractive organism and for many, they can give the creepy crawlies. The good news? The hype about tick-borne illness is mostly that: hype. While tick-borne diseases ARE a legitimate concern, there are so many layers of protection you can implement to nearly eliminate your risk. You just have to take those measures.
It also depends on where you live: there are certain places in the world where ticks are less common, where ticks are more common, where ticks might be common but not carrying pathogens that are of concern to us, where ticks are common but the species that live there are unlikely to bite humans. Remember: all of these factors must converge in order for an infection (of any kind) to take place.
Want more information on Lyme and ticks? Check out the American Lyme Disease Foundation.
I was appointed the Executive Director in 2023, but this volunteer organization has been around since the 1990s and was formed to combat growing misconceptions about Lyme disease. In contrast to patient activist groups, our team consists solely of infectious disease physicians and scientists with expertise in tick-borne pathogens, ticks, and ecology. We operate solely on donations, so support is greatly appreciated.
I hope these tips will alleviate some undue anxiety and fear that has surely been exacerbated by pop culture and media. In reality, being proactive will certainly allow you to spend time outdoors without being overly fearful.
Thanks for joining in the fight for science!
Thank you for supporting evidence-based science communication. With outbreaks of preventable diseases, refusal of evidence-based medical interventions, propagation of pseudoscience by prominent public “personalities”, it’s needed now more than ever.
Stay skeptical,
Andrea
“ImmunoLogic” is written by Dr. Andrea Love, PhD - immunologist and microbiologist. She works full-time in life sciences biotech and has had a lifelong passion for closing the science literacy gap and combating pseudoscience and health misinformation as far back as her childhood. This newsletter and her science communication on her social media pages are born from that passion. Feel free to follow on Instagram, Threads, Twitter, and Facebook, or support the newsletter by subscribing below:
Dr. Love
I was reviewing your post on LD and came upon an old note I kept. Have you come upon the following comment with regards to the antihistamine, loratidine.
Loratidine 02/10/2015 PORTOLA VALLEY, Calif. — A new study funded by the Bay Area Lyme Foundation and conducted by Stanford School of Medicine researchers has found that loratadine — may be able to help kill Borrelia burgdorferi, the bacteria associated with Lyme disease. The results of this new laboratory study show that loratadine and specifically its metabolite, desloratadine, are able to prevent manganese from entering the cell wall of the bacteria that causes Lyme disease, starving the bacteria and causing it to die in test tubes.
The antihistamine accomplishes this by inhibiting the bacteria's transport system, (Borrelia metal transporter A).
Warm regards, John