THE BAMPOT has been asked, repeatedly, to settle a dispute about which repellent actually works. This is the evidence-based answer, with no brand loyalty, no sponsorship, and no deference to marketing budgets.
DEET — the baseline
How it works: N,N-diethyl-meta-toluamide, developed by the US Army in 1946, blocks the insect's ability to detect you by interfering with its olfactory receptors. The insect cannot tell you are there — you are not masked, you are invisible to its chemical sensors. The mechanism has held up to over 70 years of testing across more insect species than any alternative.
Evidence: The evidence base is enormous and consistent. DEET is effective against mosquitoes, midges, ticks, and horseflies. At concentrations of 30-50%, it provides 6-12 hours of protection. Higher concentrations extend duration but not intensity — the point of diminishing returns is around 50%. A 2014 systematic review in the Journal of Insect Science found that concentrations above 50% offered no statistically significant increase in protection time against any tested species. The common 98-100% formulations available in outdoor shops are not providing measurably better protection than a 50% formulation; they are simply taking longer to evaporate.
Concentration and duration: The relationship is not linear. Laboratory studies using controlled conditions on human volunteers typically report:
- 10% DEET: ~1-2 hours protection
- 20% DEET: ~2-4 hours
- 30% DEET: ~5-6 hours
- 50% DEET: ~6-8 hours
- 100% DEET: ~8-10 hours
Field conditions reduce these numbers by 30-50% due to sweat, abrasion, and wind. The implication: a stated 8-hour protection is closer to 4-5 hours on an active hillwalker. Reapplication is necessary.
What the trials measured: Most efficacy studies measure "complete protection time" — the time until the first confirmed bite in a controlled environment with a known insect population. This metric overstates real-world protection because it assumes continuous exposure. In practice, the midge population varies, the wind shifts, and the user moves. A product that provides 6 hours of complete protection in a lab may provide adequate protection for a full day's walk because the conditions are not continuously at peak midge activity.
Pros: Proven across more environments and more insect species than any alternative. Works on everything — midges, ticks, clegs, mosquitoes. Inexpensive. Widely available.
Cons: The smell is industrial and persistent. Melts synthetic fabrics including nylon, polyester, and certain waterproof coatings. Damages plastics — watch straps, glasses frames, tent sealant seams, headlamp casings — on contact. Stings in eyes or on cracked skin. Not recommended for infants under two months. Some people develop skin irritation with prolonged daily use.
Effect on fabrics and gear: DEET reacts with synthetic polymers by dissolving or weakening them. Nylon tent fabric can become sticky or delaminate after repeated contact. Polyester clothing loses waterproofing. Plastics become brittle. The damage is cumulative — one exposure will not destroy a tent, but a season of DEET-contaminated hands touching the tent fabric will degrade the seam seals and coating. Practical mitigation: apply DEET to skin, not clothing, and wash hands after application before handling gear. Permethrin-treated clothing provides an alternative — the insecticide is bound to the fabric and does not damage it.
THE BAMPOT verdict: The gold standard for serious exposure — multi-day expeditions, evening fishing sessions, known high-risk areas in peak season. Overkill for a short walk. If you carry one repellent, make it Picaridin. If you carry two, make the second DEET for the occasions when the cloud is genuinely thick and the evening is still.
Picaridin — the modern alternative
How it works: Icaridin (also branded Picaridin, Saltidin) was developed by Bayer in the 1980s. It uses a different receptor pathway from DEET — binding to the insect's olfactory co-receptor rather than the odorant receptor itself — but achieves the same end result: the insect loses interest in you as a host.
Evidence: Multiple peer-reviewed studies demonstrate that 20% Picaridin is comparable to 30-50% DEET in efficacy against mosquitoes and midges. A 2015 study in the Journal of the American Mosquito Control Association tested Picaridin against Culicoides impunctatus specifically and found no statistically significant difference in protection time compared to 50% DEET at the same concentration. Duration is 6-8 hours per application.
What the trials measured: The Scottish field trials used human volunteers with exposed forearms in known midge habitat, recording time to first bite and mean number of bites over a fixed exposure period. These are more ecologically valid than lab studies because they incorporate real midge behaviour, wind variation, and temperature fluctuation.
Pros: Odourless. Non-greasy. Does not damage fabrics or plastics — it can be applied without the gear-spoiling side effects of DEET. Better skin feel means people actually apply it rather than skipping the repellent step. Safe for children from 6 months.
Cons: Slightly shorter duration than DEET — about 6 hours compared to 8-10. Less effective at lower concentrations (10% or below — check the label; some products sold as "Picaridin repellent" contain only 10%). Marginally more expensive per application. Less widely available in small Highland shops, though any outdoor retailer stocks it.
THE BAMPOT verdict: The correct default choice for most visitors. Smidge and similar Picaridin formulations cover the midge problem well, do not ruin your gear, and are pleasant enough that you will use them consistently. For most Highlands visitors, this is the one to buy.
Application technique matters more than the active ingredient
The best-performing repellent in the world is ineffective if applied incorrectly. The common failure pattern is insufficient coverage: people apply a small quantity to their hands and wipe it over their face and arms, leaving large areas of skin untreated. Midges exploit the gaps.
The correct approach is to apply repellent to all exposed skin as a thin, even film. Pay particular attention to the hairline, the back of the neck, the ears, and the wrists — the areas midges target most. The repellent needs to be on the skin, not on clothing (though Picaridin is safe for clothing; DEET is not).
Reapplication is not optional on long days. The duration estimates assume continuous coverage. Sweating, rain, and physical abrasion reduce effective protection time by 30-50%. If you are walking for more than 4 hours in active conditions, reapply.
Citronella — the folklore option
How it works: Cymbopogon nardus essential oil. The strong scent is thought to mask human odour. The mechanism is poorly understood and the evidence for efficacy is weak.
Evidence: A 2011 Cochrane Review found citronella provides short protection (around 2 hours at best) and significantly underperforms DEET and Picaridin. Citronella candles do not work outdoors in any measurable way — the smoke provides minimal effect at any distance, and the concentration of the active compound in the air is too low to affect insect behaviour.
THE BAMPOT verdict: Better than nothing for those who cannot use synthetic repellents for medical reasons. For everyone else, choose a repellent with evidence behind it.
Physical barriers vs chemical repellents
The most effective midge prevention is not a repellent at all — it is a physical barrier. A head net, long sleeves, long trousers, and closed cuffs provide complete protection without any chemical exposure. The chemical repellent is the backup for the parts of the body that cannot be covered (the face and hands) and for situations where full covering is impractical (hot weather, swimming, or when the midge activity is low enough that full covering feels disproportionate).
Permethrin-treated clothing provides a hybrid approach: the insecticide is bound to the fabric and kills or repels insects on contact, providing barrier protection without needing to apply repellent to the skin. Permethrin treatment is effective against ticks as well as midges and lasts through multiple washes. It is not a replacement for skin-applied repellent — it protects the covered areas only — but it reduces the total area of skin that needs repellent.
The bottom line
| Repellent | Efficacy | Duration | Gear risk | Best for |
|---|---|---|---|---|
| DEET 50% | Excellent | 6-8h | Melts synthetics | Serious exposure, expeditions |
| Picaridin 20% | Excellent | 6-8h | None | Day-to-day use, most visitors |
| Citronella | Poor | 1-2h | None | Last resort, no synthetics tolerated |
| Lemon eucalyptus | Moderate | 3-4h | None | Natural alternative seekers |
| Permethrin (clothing) | Good (barrier) | Multiple washes | None on gear | Ticks + midges, baseline protection |
THE BAMPOT's recommendation: Picaridin for day-to-day use, DEET for serious exposure. Treat clothing with permethrin for tick and midge baseline protection. Head net for evenings. The combination of all three provides more protection than any single repellent at any concentration. And none of it works if you leave it in the car.