Mattress protectors and encasings: what they do and don't do

A fitted mattress protector and a zippered encasing do different jobs. The protector catches spills, sweat and stains. The encasing wraps all six sides in fabric tight enough to block allergen. Encasings reliably cut mite allergen in mattress dust; what they do for symptoms is genuinely mixed. Two large adult trials found no benefit when encasings were the only measure, while a trial in children with asthma found fewer hospital visits. Allergy guidance recommends them as one part of a wider plan. Here's the honest picture, and how to choose.

General information about mattress covers and allergens, not medical advice. If you have allergies or asthma, follow your clinician's plan.

Two products with one name problem

Shops use "protector," "cover" and "encasement" loosely. The practical distinction is coverage and fabric.

A protector is usually fitted like a deep sheet, with a waterproof membrane or absorbent layer on top. It covers the sleeping surface and often the sides, leaving the underside open. It's built to keep liquids and soil off the mattress. It isn't usually rated as an allergen barrier.

An encasing zips around the whole mattress, box spring or pillow. An allergy practice parameter describes four types: vinyl, laminates, woven microfiber and nonwoven microfiber. Vinyl and laminates block all allergens but don't let air or water vapor through, so they're uncomfortable and now rarely used. Woven microfiber is the common choice: tightly woven ultrathin filaments act as a filter while staying breathable. The parameter advises against nonwoven covers because they can't be washed and accumulate allergen. Our encasement article covers the fabric types in more depth.

Why pore size matters

According to the practice parameter, woven fabrics with a mean pore size smaller than 10 microns block the main mite allergen, Der p 1, while blocking cat allergen needs pores smaller than 6 microns. If you're buying an encasing for allergy, look for a stated pore size and a washable woven fabric. A fitted protector won't have either, because that's not its job.

The zipper and seams count too. A barrier fabric with a gap at the zipper end leaks at the gap. Encasings with a flap or zipper cover, sized to fit snugly, close that route.

What the trials found

The trials are worth reading carefully, because they're often summarized as either a clear success or a clear failure. Both are oversimplified.

Allergic rhinitis, 2003. Terreehorst and colleagues gave 279 patients with mite-sensitive allergic rhinitis either impermeable or ordinary covers for mattress, pillow and duvet for a year. Mite allergen in the mattresses fell significantly in the impermeable group, but there was no significant effect on symptoms. The authors concluded that "this single avoidance measure did not lead to a significant improvement" in rhinitis symptoms.

Asthma in adults, 2003. Woodcock and colleagues ran a double-blind trial of allergen-impermeable bed covers in 1,122 adults with asthma. Mattress allergen fell in the active group, but lung function and the ability to reduce inhaled steroids didn't differ. Encasings as a single measure didn't help these adults.

Asthma in children, 2017. Murray and colleagues randomized 284 mite-sensitized children aged 3 to 17, all recruited after an emergency hospital visit for asthma, to real or placebo encasings for a year. Fewer children in the encasing group attended hospital with an exacerbation: 29.3% versus 41.5%. In adjusted analysis the risk was 45% lower. The annual rate of such visits was lower too but not statistically significant, and there was no difference in courses of oral steroids.

Reviews. A Cochrane review of rhinitis trials found that only two encasing studies were of good quality and the rest "small and of poor quality." A 2024 meta-analysis grouped encasings with hot-washing bedding as "partial bedroom control" and concluded that "partial bedroom control is not recommended" as a strategy on its own, while combined bedroom measures showed more promise.

What the guidance says

The 2013 practice parameter recommends encasings, but with a clear caveat: encasings "effectively contain mite allergens," yet covers alone are unlikely to bring a benefit unless used as part of a broader avoidance plan. That's consistent with the trials: the allergen drops, and the effect on symptoms depends on who you are and what else you do.

One transparency note the parameter itself makes: one workgroup member owned a company that sells a product discussed in it, so the encasing section was rewritten by other members without his participation. We mention it because the document does.

Choosing and using them

• For spills, sweat and stains: a washable fitted protector. Wash it regularly, more often with pets, children or night sweats.
• For mite allergy: a woven encasing with a stated pore size, on the mattress, box spring and pillows, as part of the plan your allergist suggests.
• For both: encasing first, protector over it. The protector takes the daily mess; the encasing stays on as the barrier.
• Fit: snug, with the zipper fully closed and covered. Check for tears every time you change the bed.

Washing schedules for each are in how often to wash sheets and protectors.

A protector or encasing also keeps a topper cleaner if it goes over the top layer; toppers covers which fills can go in a washer and which can't.

What neither one does

A protector or encasing keeps new soil and allergen from moving between you and the mattress. Neither removes what was already in the mattress before it went on, and protectors don't cover everything. If the bed was uncovered for years, had an accident get through, or smells, cleaning still has a job; is cleaning worth it with a protector? works through that. More care questions are in the hub.

Sleep Sanitation's view

This section is our view. We recommend a washable protector on every bed, and a woven encasing where someone is mite-allergic and their allergist agrees. We don't sell either, and we don't think a cleaning replaces them. When a protected or encased mattress needs attention, our visits use dry vapor steam with little water, HEPA vacuuming and UV-C light, and include a moisture check after service and the built-in bed mite sensor on our UV-C vacuum. See how we're different or call or text (402) 512-5658.

What we don't know

• Why encasings helped children with severe asthma in one trial but not adults in others. Age, severity and exposure levels all differed.
• How much an ordinary fitted protector reduces mite allergen exposure. Trials tested barrier encasings, not spill protectors.
• How well encasings hold their barrier after years of washing and use in real homes.

Changelog

• 7 October 2026: First published. Sources accessed on this date.