Screen doors and windows: the simplest mosquito barrier that works

Why screens are the first thing to fix

Mosquitoes that bite indoors at dusk and at night are responsible for a large share of household exposure to mosquito-borne illness. Closing the openings in a home is the lowest-effort, lowest-cost barrier a household can put in place. Fine-mesh screens on doors and windows reduce indoor mosquito density without chemicals, without electricity, and without ongoing maintenance beyond an annual check.

The World Health Organization lists physical barriers — including fitted screens — among the core interventions in its global vector control response. They work because they remove the opportunity rather than trying to interrupt it after a mosquito is already inside.

What "fine-mesh" actually means

A screen is only as useful as its mesh size. The relevant measure is holes per inch (or, equivalently, hole diameter in millimetres). For mosquito control:

• 18x16 mesh is the floor. This is what most off-the-shelf insect screens use.
• 20x20 or finer is preferred where smaller biting flies are a concern.
• Below 16 holes per inch, larger insects pass through and the value drops fast.

Material matters too. Fibreglass is the cheapest and easiest to retrofit. Aluminium lasts longer but is heavier and harder to install. Stainless steel is the longest-lived but is overkill for a typical European household.

Where to install

Three openings get missed more often than they should:

1. Bathroom and kitchen vents. These are warm and humid, exactly where indoor mosquitoes look for resting spots during the day.
2. Doors that open onto balconies or gardens. A single unguarded door undoes every screened window on that floor.
3. Roof skylights and clerestory windows. Ignored because they're hard to reach. Fitted screens on a gas-strut frame solve this.

For households retrofitting an existing home, doors and ground-floor windows give the most reduction in indoor exposure per unit of effort.

What screens do not solve

Screens do not eliminate outdoor exposure on a balcony, in a garden, or on a terrace at dusk. They do not prevent breeding in standing water around the home — that requires source reduction, which is a separate intervention. And a torn screen is worse than no screen, because it gives the household false confidence; an annual visual check at the start of mosquito season takes ten minutes and catches almost all real failures.

A simple yearly checklist

• Walk every door and window at the start of the season; inspect each screen visually.
• Replace any mesh with visible tears, gaps at the frame, or detached corners.
• Confirm vent covers and skylight screens are still in place.
• Note the date and any replacements somewhere durable, so next year's check is faster.

Good screens are the kind of intervention that disappears once installed. That is the point.