Bug spray is one of those products almost everyone owns and almost no one can explain. You spray it on, the mosquitoes leave you alone, and that is usually where curiosity ends. But the way repellents actually work is more interesting, and more reassuring, than most people assume. The leading actives recognized by public health authorities, including DEET, picaridin, and PMD from lemon eucalyptus, do not poison insects or kill them on contact. They work by interfering with the sensory cues that lead a mosquito to your skin in the first place.
At The Superbloc, our Bloc Off Spray is built on 8 percent PMD (para-menthane-3,8-diol) derived from lemon eucalyptus, one of the actives the CDC recognizes alongside DEET and picaridin. Because we formulate and test this product ourselves, we spend a lot of time explaining the science to customers who want to understand what they are putting on their skin. This guide is that explanation, written plainly.
The quick answer
Bug spray works by masking and disrupting the signals mosquitoes use to locate a human host. Mosquitoes track you using exhaled carbon dioxide, body heat, moisture, and the specific blend of compounds on your skin. Repellent actives such as DEET, picaridin, and PMD create a vapor barrier just above the skin that confuses those sensors, so the mosquito either cannot lock onto you or finds you unappealing to land on. Repellents are not insecticides. They do not kill mosquitoes. They wear off over time mainly because the active ingredient evaporates, which is why concentration and reapplication both matter.
How mosquitoes actually find you
Before you can understand how a repellent interferes with a mosquito, it helps to know how a mosquito finds you in the first place. It is not random, and it is not really about "sweet blood." Mosquitoes are guided by a layered set of cues that switch on at different distances.
Carbon dioxide, from far away
The first thing a mosquito detects is carbon dioxide. Every time you exhale, you release a plume of CO2, and mosquitoes can sense it from many feet away. CO2 does not tell the mosquito exactly where you are, but it flips a switch that says a warm-blooded host is nearby and worth investigating. This is why simply breathing makes you a target, and why a group of people gives off a stronger signal than one person alone.
Body heat and moisture, up close
As the mosquito flies closer, it starts reading heat and humidity. Your body is warmer than the surrounding air and gives off water vapor from your skin. These cues help the mosquito zero in during the final approach, in the last few feet where CO2 alone is too diffuse to be precise.
Skin odors, at landing range
The most personal cue is the smell of your skin. Human skin produces a complex mixture of compounds, including lactic acid, ammonia, and various fatty acids created by the bacteria that live on us. This blend is different for every person, which is a large part of why some people genuinely do get bitten more than others. At close range, this scent signature is what tells a mosquito to land and probe rather than move on.
Put together, a mosquito's search looks like a funnel. CO2 draws it into the area, heat and moisture narrow the approach, and skin odor confirms the target. A good repellent interrupts that funnel.
How repellents disrupt those cues
Here is the part that surprises people. Modern repellents do not build a physical force field, and they do not harm the insect. They work at the level of the mosquito's senses.
When you apply a repellent, the active ingredient slowly evaporates off your skin and forms a thin layer of vapor in the air just above it. That vapor is what the mosquito encounters first. Two things happen. The active can interfere with the mosquito's odor receptors, the tiny biological sensors on its antennae that read the compounds coming off your skin. And the vapor can effectively mask your natural scent, so the cues that normally say "land here" are muddled or hidden.
The net effect is that the mosquito loses the trail. It may still be drawn toward your CO2 and warmth from a distance, but as it closes in, the signals it relies on to commit to a bite are scrambled. Many mosquitoes simply do not land. Others land briefly and leave without biting because the surface does not read as a suitable host. This is why you may still see mosquitoes around you while wearing repellent even though you are not getting bitten. The repellent is doing its job at the decision point, not clearing the air of insects.
Do repellents kill mosquitoes?
No, and this is worth stating clearly because it is a common misunderstanding. Repellents and insecticides are different categories of product. An insecticide is designed to kill insects. A repellent is designed to keep insects away from a surface, in this case your skin, by disrupting the cues they use to find and choose a host. When you apply Bloc Off Spray, you are not spraying a poison and you are not killing anything. You are making yourself harder to detect and less appealing to land on. That distinction is the whole reason repellents can be formulated for everyday personal use.
How the main actives compare
Public health authorities point to a short list of actives with a solid track record. The three most relevant to personal skin application are DEET, picaridin, and PMD from lemon eucalyptus. They all share the same basic job, disrupting host-seeking cues, but they differ in origin and feel.
How does DEET work?
DEET (N,N-diethyl-meta-toluamide) is the oldest and most studied synthetic repellent, in wide use since the mid twentieth century. It works the way described above, forming a vapor layer that interferes with a mosquito's ability to detect and settle on skin. DEET is effective and long-lasting at higher concentrations. Its main drawbacks are sensory rather than safety related for most adults. It can feel greasy, carries a distinct smell, and at higher concentrations can affect certain plastics and synthetic fabrics, which is why some people prefer an alternative for everyday wear. For a fuller side-by-side, see our guide on <a href="/blogs/news/picaridin-vs-deet-2026-how-the-two-repellent-actives-compare">how picaridin and DEET compare</a>.
How does picaridin work?
Picaridin is a synthetic active modeled loosely on a compound found in black pepper plants. Functionally it behaves much like DEET, masking and disrupting the cues mosquitoes rely on, but many users find it more pleasant to wear. It tends to be lighter, close to odorless, and less likely to interact with gear and clothing. It has become a popular DEET alternative for people who want comparable protection with a better feel on the skin.
How does PMD work?
PMD (para-menthane-3,8-diol) is the active we use in Bloc Off Spray, and it is the one active on the CDC's recognized list that comes from a plant source, the lemon eucalyptus tree. PMD is the refined, standardized compound responsible for the repellent effect in oil of lemon eucalyptus. It works on the same principle as the synthetics, creating a vapor barrier that interferes with the mosquito's odor receptors and masks your natural scent, so host-seeking cues get disrupted at close range. The appeal of PMD is that it delivers protection comparable to the well-known synthetics while being plant-derived and, for many people, more pleasant to wear. We go deeper on this active in our explainer on <a href="/blogs/news/lemon-eucalyptus-mosquito-repellent">lemon eucalyptus as a mosquito repellent</a>.
One important note. PMD, the concentrated and refined active, is not the same as unrefined essential oils marketed as "natural" repellents. The refinement and standardization are what make PMD reliable and testable, which is why it earns a place alongside DEET and picaridin rather than in the loose category of scented oils that may smell pleasant but offer little real protection.
Why bug spray wears off
If a repellent worked forever, you would apply it once and forget it. It does not, and the reason comes straight from how it works. The protection depends on that thin layer of active vapor sitting above your skin. Anything that removes the active from your skin shortens the window of protection.
The biggest factor is simple evaporation. The active is slowly leaving the surface of your skin the entire time, which is what creates the protective vapor, but it also means the supply is steadily depleting. On top of that, sweat, water, rubbing against clothing, swimming, and toweling off all strip active from the skin faster. Heat and heavy activity speed this up. This is why a repellent that protects for several hours on a calm evening may need earlier reapplication on a hot, active, sweaty afternoon.
Why concentration matters
Concentration is essentially the size of the reservoir. A higher percentage of active means more of it sitting on your skin, which generally translates to a longer protection window before the vapor layer thins out too much to be effective. This is why concentration, not brand marketing, is one of the more honest signals of how long a product will last. Our Bloc Off Spray uses 8 percent PMD, a level our own lab testing supports for 6 or more hours of protection under typical conditions. Higher concentration mainly buys duration, not a stronger instant effect, so the right choice depends on how long you need to stay covered.
Why reapplication matters
Because the active depletes, reapplication is not a sign that a product is weak. It is how repellents are meant to be used. Follow the reapplication timing on the label, and reapply sooner if you have been sweating heavily, swimming, or toweling off. A common mistake is applying too thin a coat or missing spots such as ankles and the backs of the knees, which mosquitoes readily target. Even coverage matters as much as the number on the bottle.
Where PMD and The Superbloc fit
We built The Superbloc around a straightforward idea. People want protection they can trust and a product they will actually want to wear, without a heavy chemical feel or smell. PMD from lemon eucalyptus let us do both. It is recognized by the CDC alongside DEET and picaridin, it is plant-derived, and in our testing it holds up for 6 or more hours.
Bloc Off Spray is alcohol-free and water-based, which keeps it gentle on skin and comfortable to reapply through the day. Based on our own brand testing, it is suitable for use from 6 months of age. We want to be precise here rather than oversell. General EPA and CDC guidance advises that oil of lemon eucalyptus and PMD products are not recommended for children under 3 years old, so our from-6-months guidance reflects our specific formulation and testing, not a blanket rule for the category. If you have a young child, read the label and talk to your pediatrician.
For everyday coverage, most people reach for the <a href="/products/bloc-off-spray">Bloc Off Spray</a>. For households with kids or anyone who wants a wipe option for faces and travel, the <a href="/products/family-protection-pack">Family Mosquito Protection Pack</a> pairs the spray with our Bloc Off Wipes. And if what you care about most is not smelling like traditional bug spray, our roundup of the <a href="/blogs/news/best-smelling-mosquito-repellent">best smelling mosquito repellent</a> options is a good place to start.
Frequently asked questions
Does bug spray kill mosquitoes? No. Bug spray meant for your skin is a repellent, not an insecticide. It works by masking and disrupting the cues mosquitoes use to find and land on you, so they cannot lock onto you or find you appealing. It does not poison or kill them. That is exactly why it can be formulated for regular personal use.
How does bug spray actually keep mosquitoes away? The active ingredient evaporates slowly off your skin and forms a thin vapor layer just above it. That vapor interferes with the odor receptors on a mosquito's antennae and masks your natural scent. The mosquito loses the trail of cues it needs to commit to a bite, so it usually does not land.
Why does bug spray stop working after a few hours? Protection depends on active ingredient sitting on your skin, and that active steadily evaporates. Sweat, water, rubbing, and heat remove it faster. Once the vapor layer thins out, the protection fades, which is why reapplication and adequate concentration both matter.
How is PMD different from regular essential oils? PMD (para-menthane-3,8-diol) is the refined, standardized active found in lemon eucalyptus, and it is recognized by the CDC alongside DEET and picaridin. Unrefined essential oils sold as natural repellents may smell nice but are not standardized and generally offer weak, short-lived protection. The refinement is what makes PMD reliable and testable.
Is a higher concentration of repellent stronger? Higher concentration mainly means longer-lasting protection, not a more powerful instant effect. A larger percentage of active gives you a bigger reservoir on your skin, so the vapor layer stays effective longer before you need to reapply. Choose your concentration based on how long you need to stay covered.
Last updated: 2026-07-06. Sources: U.S. Centers for Disease Control and Prevention (CDC) guidance on mosquito repellents; U.S. Environmental Protection Agency (EPA) repellent guidance; The Superbloc internal lab testing of Bloc Off Spray. By Tanya Lee, Co-Founder of The Superbloc, with Cassidy Huang, Co-Founder and Formulator.