Convexity is a curve on the skin side of a barrier or accessory that applies gentle pressure around the stoma, pushing the stoma opening above the level of the barrier edge so output drops into the pouch instead of tracking sideways. An international consensus of stoma care nurses lists a stoma at or below skin level, an off-centre opening, creases and gullies in the peristomal skin, and liquid output as indicators for it.
Most people meet convexity after months of leaks that no amount of paste, tape or ring will fix, because the problem was never the seal. It was the shape.
Convexity is also the one ostomy decision that deserves a stoma nurse rather than a forum, and the reason for that is in the risks section below.
In this article
- What convexity is
- When it is indicated
- How it is assessed
- Soft vs firm
- Belts and convexity
- Risks to watch
- Trying convexity
- Frequently asked questions
What does convex mean on an ostomy product?
A curve on the skin side of the barrier, defined in the clinical consensus as "a curvature on the skin side of the barrier or accessory."
A flat barrier sits level on the abdomen. A convex barrier bows outward toward the skin, so when you press it on, it pushes the peristomal skin down and the stoma up. That change of a few millimetres decides whether output lands in the pouch or runs under the seal.
Convexity turns up in three forms, and they can be combined: a convex wafer or baseplate, a convex insert that sits under a flat wafer, and a convex barrier ring like the one we stock. The consensus notes the effect is stronger when the convexity sits close to the base of the stoma.
Convexity solves a shape problem. If your stoma sits proud and your skin is even, a flat barrier plus a flat ring is the simpler and kinder answer.
When is convexity indicated?
The 2017 international consensus meeting on convexity, published in the Journal of Wound, Ostomy and Continence Nursing, agreed a set of indicators. These are the ones patients recognise in themselves.
| Indicator | What it looks like day to day |
|---|---|
| Stoma opening at skin level | Output pools at the base instead of dropping away |
| Stoma opening below skin level | The stoma sits in a dip and undermines the seal on one side |
| Off-centre stoma opening | Output consistently escapes toward one direction |
| Creases, folds, bulges or gullies | The wafer bridges a channel that output follows |
| Liquid output | Named in the consensus as an indicator, to prevent and manage leakage |
| A stoma that telescopes | Retracts and protrudes as you move or cough |
The consensus also confirms convexity can be used with a colostomy, an ileostomy or a urostomy, so stoma type is not the deciding factor. Shape is.
Hollister 89601 CeraRing oval convex barrier rings, 10 pack. Adds convexity right where the consensus says it works hardest, at the base of the stoma, with a ceramide-infused barrier. FSA and HSA eligible.
How is the need for convexity assessed?
With the pouching system off, sitting down. Both details come straight from the consensus statements.
Assessment standing up, with the appliance on, misses the thing you are looking for. Skin that reads as flat while standing folds into a gully when you sit, and that gully is where the leak comes from.
- Remove the pouching system and clean the skin, since the consensus states the system must be off to assess properly.
- Sit down, the position the panel named as best for assessment.
- Look at stoma height at the base, not the tip, and note whether it sits above, at, or below skin level.
- Feel the peristomal plane with a flat hand for dips, creases and firmness.
- Note your output type, since liquid output is itself an indicator.
- Take photos sitting and standing to show your stoma nurse, which shortens the conversation considerably.
The panel was direct about who should make the call: the stoma care nurse is best prepared to advise on the appropriate use of convexity.
Soft or firm convexity: how do you choose?
Match the barrier to the abdomen, not to the severity of the leak.
The consensus gives a rule that reads backwards at first: "With a firm peristomal region, soft convexity can be a better option than firm convexity," and "with a soft peristomal region, firm convexity can be a better option than soft convexity."
| Your abdomen | Usually suits | Why |
|---|---|---|
| Firm, toned, little give | Soft convexity | It flexes with you instead of fighting a rigid surface |
| Soft, creased, changes with position | Firm convexity | It provides the structure the abdomen does not |
| Recent surgery, tender skin | Discuss with your nurse first | Pressure on healing tissue needs supervision |
| Parastomal hernia | Specialist assessment | Convexity over a hernia can press where it should not |
Depth of convexity varies between products as well, from shallow to deep. That is another reason this is a fitting conversation rather than an online purchase decision.
Does an ostomy belt help?
Yes. The consensus states plainly that a belt can be used to enhance the effect of convexity. It adds even pressure across the barrier so the curve stays seated as you move.
We do not stock belts, so this comes from your supply provider. If you use one, keep the tension moderate: a belt tight enough to hurt is applying more pressure than the barrier needs, and pressure is the thing to watch with convexity.
What are the risks of convexity?
Sustained pressure on skin can cause damage, so the consensus asks for a check at every appliance change.
The statement is specific: assessment of harmful effects of convexity, such as ulceration and pain, is needed with each pouching system change. Published cases also describe recurrent lesions under convex surfaces in parastomal pyoderma gangrenosum.
- Pressure marks or ulceration in a ring shape matching the barrier edge.
- Pain under the barrier rather than at the stoma itself.
- Skin that stays indented for a long time after removal.
- Bruising around the peristomal skin.
- Any new sore that appears under the convex area and returns after each change.
Look at the skin every single change, in daylight, before the new appliance goes on. Convexity is safe when it is monitored and risky when nobody looks.
What if you want to try convexity now?
A convex barrier ring is the lower-commitment way in, because it adds convexity at the stoma base without changing your whole pouching system. It also comes off easily if your skin reacts.
We stock the Hollister 89601 oval convex CeraRing. We do not stock convex wafers, convex inserts or belts, so if your nurse recommends a full convex system, your supply provider will be the source for that part.
Hollister 89601 CeraRing oval convex barrier rings, 10 pack. Convexity at the stoma base under your existing flat wafer, with a ceramide-infused barrier. FSA and HSA eligible.
Hollister 8805 Adapt CeraRing barrier rings, 4 inch, 10 pack. Before moving to convexity, a wide flat ring properly moulded into the creases solves a surprising share of leaks. FSA and HSA eligible.
For the ring-level comparison, see convex vs flat barrier ring. The consensus itself is published as Use of Convexity in Ostomy Care: Results of an International Consensus Meeting.
Frequently asked questions
What is a convex ostomy system?
A pouching system where the skin side of the barrier curves outward, applying pressure around the stoma so the stoma opening sits above the barrier edge. It is used when a stoma is flush or retracted, or when peristomal creases undermine a flat seal.
When should you use convexity?
The international consensus lists a stoma opening at or below skin level, an off-centre opening, creases, folds or gullies in the peristomal skin, and liquid output as indicators. A stoma care nurse should confirm the fit.
Is soft or firm convexity better?
It depends on your abdomen. The consensus suggests soft convexity for a firm peristomal region and firm convexity for a soft one, so the barrier compensates for the abdomen rather than matching it.
Can convexity damage the skin?
It can if it is not monitored. The consensus asks for assessment of harmful effects such as ulceration and pain at every pouching system change. Check the skin in daylight before each new appliance goes on.
Does a belt help with a convex barrier?
Yes. The consensus states a belt can be used to enhance the effect of convexity, by keeping even pressure across the barrier as you move.
Can I get convexity without changing my whole system?
Yes. A convex barrier ring adds convexity at the stoma base under your existing flat wafer, which is a smaller change than switching to a convex baseplate.
Convexity where it works hardest
Hollister 89601 oval convex CeraRing, FSA and HSA eligible, with free US shipping over $80.
Shop convex rings →This guide is general information, not medical advice. Convexity should be assessed by a stoma care nurse, and the skin under it checked at every change.