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Ostomy and Convexity

Convexity refers to the outward shape of the faceplate, similar to the top of a bell, intended to reach inside the peristomal skin for maximum seal around the stoma.

Why Convexity in Ostomy Appliances?

Convexity in Ostomy Appliances exists to provide optimal peristomal seal. A stoma can have uneven shape, unusual size, and irregularities around the peristomal skin area which render non-convex ostomy systems ineffective. A convex ostomy bag system curves outwards. With that profile, it can press the peristomal skin to protrude the stoma enough for the ostomy bag to attach securely and firmly.

 “One of the guiding principles of ostomy care is to establish and maintain a secure and predictable seal. Products that incorporate convexity are often considered an important tool for achieving this goal. Convexity is defined as A curvature on the skin side of the barrier or accessory. Convex products are frequently cited as the preferred means to manage flat or retracted stomas and to compensate for irregular peristomal planes such as creases or folds. Although a variety of convex products are available with different depths and shapes, there is little supporting evidence to guide their selection and use.

The origins of convex product development are not known. Limitations in early ostomy product availability and the need to cope with poorly constructed stomas or irregular body contours were historically addressed by creative use of pastes, belts, rings, and medical adhesives. During the 1980s and early 1990s, multiple ostomy product manufacturers designed and released firm convex skin barriers designed for both 1- and 2-piece pouching systems. More recently, manufacturers have introduced additional accessories with convex features such as barrier rings and soft convex skin barriers.

Although the terms “convex” and “convexity” are consistently used to describe the curvature on the adhesive side of the skin barrier or accessory, other descriptors remain undefined. There are no industry standards for the depth, profile, tension, firmness, softness, and flexibility of products with a convex feature. Research and clinical practice guidelines for product selection are lacking, which leaves the determination of matching stomal protrusion and peristomal contours to appropriate barriers to the individual knowledge and skill of the clinicians.”1

What is a Convex Pouching System?

“There are flat and convex pouching systems. A flat pouching system lies flat on the skin around a stoma. A convex pouching system is different because a skin barrier, faceplate, or ring curves outward against the skin. The outward curve presses down on the skin. The outward curve presses down on the skin and causes a person’s stoma to stick out more an better empty into the pouching system.

Why use a convex product?

  • Convex products may:
  • Stop urine or stool leakage.
  • Make you feel more comfortable and secure.
  • Prevent or stop skin irritation.
  • Improve wear time of pouching system.
  • Save your time and money.

When may a convex product be used?

Convex products may be used to:

  • Prevent frequent pouch leakage caused by: A stoma that empties at or below skin surface. Wrinkles, scars, or creases in the skin near the stoma. Very soft abdomen around the stoma.
  • Improve wear time for patients who have 3 days or less wear time with a flat pouching system.

What else should I know about convex products?

  • A convex pouching system should be fitted by a WOC/ET nurse.
  • A follow-up visit may be needed to make sure the convex pouching system is working for you.
  • Convex products may leave a mark on your skin.
  • If you use a belt, it should be snug but not too tight.
  • Some convex products may be less flexible and less comfortable than nonconvex products.
  • Depending on the appearance of your stoma and abdomen, a convex pouching system with a shallow, medium, or deep outward may be needed. Some convex products may be more expensive than flat products but may save money if longer wear time is possible.
  • A convex pouching system is not the solution for all leakage problems. It is important to see a WOC/ET nurse so he or she can recommend a pouching system that is right for you.

What are the different types of convex Products?

Cut-to-fit convex: This is a one- or two-piece pouching system that allows you to cut the opening in the skin barrier to fit your stoma. This is especially recommended if your stoma is not round.

Precut convex: This is a one- or two-piece pouching system that has various-sized openings in the skin barrier.

Convex insert: These presized plastic rings are for use in the flange of a flat two-piece pouching system.

Barrier strips/rings: These products can be molded to different shapes or sizes.

Custom-made convex product: A product with built-in convexity that is made for you by a special company.

Faceplate: This is a reusable product with built-in convexity.

Ostomy belts and binders: These products may be used to give you extra support.”2

The ideal convex system should deliver the following:

  • Avoid ostomy leaking.
  • Adapt naturally to the peristomal skin contour while sustaining the movements and tensions caused during normal wear.
  • Support a healthy peristomal skin area.
  • Feel comfortable and secured.
  • Increase ostomy bag wear.

When to recommend Convex Bag Systems?

Patients should wear convex ostomy bag systems for two months from discharge or after the stoma reaches its normal size. Currently, patients wear convex products more often in the presence of the following situations:

  • Retracted stoma. “The retracted stoma discharges effluent at the skin level and causes peristomal irritation and is more prone to leakage. Acute retraction in a freshly created stoma can result in dehiscence of the mucocutaneous junction and intraperitoneal contamination. Functionally, a retracted loop stoma is problematic, as its ability to fully divert the fecal stream is compromised. Retraction is caused by excess tension placed upon the matured segment of bowel, which is typically the result of inadequate mobilization. As such, attempts at local revision may not succeed because the underlying cause of the tension cannot be fully addressed through a peristomal incision. Laparotomy is usually needed to gain more length and to revise the stoma in a tension-free manner.”3
  • Flush stoma and Peristomal skin level stoma. “With a flush or skin-level stoma, however, it is important to select a barrier that is resistant to breakdown by urine. Urine from a flush stoma constantly washes over the barrier, and a barrier that is not resistant to urine quickly deteriorates. When a pouch barrier is changed, the barrier and the peristomal skin are assessed to ascertain that the barrier is not absorbing the urine and causing peristomal maceration.”4
  • High output stoma. “High stomal output can erode the solid skin barrier causing the pouching seal to leak. An important assessment of stomal function includes the amount of output. Patients can relate this by describing the amount of times the pouch is emptied in 24 hours and by describing the consistency of output. Normal ileostomy output should be approximately 1,000 cc/24 h with pasty consistency comparable to loose oatmeal.”5
  • Most loop ostomies. “A loop ostomy is formed when a loop of bowel is brought up to the skin, and an incision is made on one side. The distal end is sutured to the skin, whereas the proximal side of the loop is everted back on itself. The result is a stoma with two openings: the proximal (functional) limb from which the effluent or stool is discharged, and the distal limb, which may connect to the anus and secrete mucus. A loop ostomy is used most often when a temporary ostomy is formed.”6
  • Peristomal skin creases, wrinkles, or scars. “The stoma location on the abdomen and the stoma height or protrusion above the surrounding skin surface is very important to determine the success of managing an ostomy appliance, especially for high-volume and/or very liquid output. Even though these properties of the stoma cannot readily be changed, it is important to understand how they affect the success of failure of a pouching system. Ideally, the stoma should have a profile above the skin of about 2cm, with the os/lumen located at the apex/top of the stoma. Situated this way, effluent is directed out and down into the pouch system. Stomas located in skin folds, near scars or incisions, with low profiles, and/ or the lumen off-center or at skin level contribute to leaks and erosion of the barriers.”7
  • Excessive ostomy bag changes
  • Ostomy Leaks
  • Flimsy abdomen

When to Discourage Convex Bag Systems?

Consult with your ostomy professional before adopting this type of appliance. If rashes, bleeding, pain or itching develop with use, discontinue and seek professional advice, since these could be symptoms of conditions that require immediate treatment. These conditions are:

  • Peristomal Pyoderma Gangrenosum. “Pyoderma gangrenosum is a rare inflammatory skin disease characterized by painful ulcers with well-defined erythematous or violaceous undermined borders. Approximately 0.5-2 % of patients with ant-inflammatory bowel disease can develop peristomal pyoderma gangrenosum. […] Peristomal pyoderma gangrenosum can be seen in approximately 0.6 % of ostomates; however, some postulate the actual incidence may be higher due to underdiagnosis. For unclear reasons, peristomal pyoderma is associated with female gender, autoimmune disorders, and obesity in IBD patients.”8
  • Peristomal Varices. “These varices may bleed spontaneously, and the bleeding may be dramatic. Treatment modalities that may initially be effective in achieving hemostasis include injection sclerotherapy, percutaneous transhepatic coil embolization, surgical stomal revision, and transjugular intrahepatic portosystemic shunt placement. Nevertheless, recurrent bleeding is common, and liver transplantation should be considered to relieve portal hypertension and treat the underlying liver disease.”9
  • Peristomal Ulcers. “Peristomal ulcers, regardless of etiology, present a challenging clinical situation. It is necessary to dress the wound, manage the wound exudate and develop an effective pouching system. Because exudate from the peristomal wound interferes with ostomy appliance adherence, peristomal ulcers have traditionally been managed with nonadherent pouching systems. Recent advances in wound care products have expanded the range of Overview treatment options for peristomal ulcers which provide security, extended wear-time and cost-effectiveness.”10
  • Mucocutaneous separation. “Stoma retraction and separation of the mucocutaneous border can occur as a result of trauma or tension on the internal bowel segment used for the creation of the stoma. In addition, mucocutaneous separation can occur if the stoma does not heal as a result of the accumulation of urine on the stoma and mucocutaneous border. Using a collection drainage pouch with an antireflux valve is helpful because the valve prevents urine from pooling on the stoma and mucocutaneous border. Meticulous skincare to keep the area around the stoma clean and dry promotes healing.”11

What Do Manufacturers Offer in Terms of Convexity?

Users can attain convexity in numerous ways. Most manufacturers have convex barriers to fit two-piece pouch systems and convex one-piece ostomy pouches. Additionally, pre-cut and cut-to-fit options are available for regular and irregular stoma shapes respectively.

This is a compilation of various products from different brands available in the market.


Makes the Premier One-Piece and the New Image Two-Piece ostomy bag systems. The first one is convex, and the second uses the New Image skin barrier. Users can manage further adjustments with Adapt Convex Barrier Rings. These come in round and oval shapes and one can be placed on top of each other to adjust to the ostomy bag system. They serve to reach deep or flexible convexity.


This brand has the Active Life One-Piece Convex line that includes the ostomy bag and the convex barrier into one unit. It counts also with the Durahesive Skin Barrier, moldable to the skin’s contour.


SenSura one and two-piece ostomy pouches come with convex faceplates in pre-cut or cut-to-fit options.


Microskin from Cymed is not a convex accessory per se, but its properties to adjust to almost any peristomal skin contour make it a suitable choice.


A parastomal ostomy belt provides extra firmness and pressure for optimum convex fit. Nu-hope also has an extensive selection of ostomy belts.

Convex alternatives vary in depth: shallow, moderate, and deep, as well as in texture: firm and soft. Selecting one versus another has various implications. Ostomy nurses should help determine the right choice through an evaluation of your situation. Achieving convexity might take time and size adjustments with convex inserts, barrier rings, convex wafers, strips or pastes. Whichever combination works, it requires close monitoring to ensure that it meets the objectives from convexity. Once patients become familiar with the process, they may try other variants. Seek an ostomy nurse if you have any questions or requirements.


(1) Hoeflok, J., Salvadalena, G., Pridham, S., Droste, W., McNichol, L., & Gray, M. (2017). Use of convexity in ostomy care: Results of an International Consensus Meeting. Journal of Wound, Ostomy, and Continence Nursing, 44(1), 55. Available online at

(2) Colwell, J. C., Goldberg, M. T., & Carmel, J. E. (2012). Fecal & Urinary Diversions-E-Book: Management Principles. Elsevier Health Sciences. Available online at

(3) Kwiatt, M., & Kawata, M. (2013). Avoidance and management of stomal complications. Clinics in colon and rectal surgery, 26(02), 112-121. Available online at

(4) Balachandar, T. G. (2018). Stoma Care. Available online at

(5) Bayless, T. M., & Bayless, T. M. (2014). Advanced Therapy of Inflammatory Bowel Disease: Ulcerative Colitis (Volume 1), 3e (Vol. 1). PMPH-USA. Available online at

(6) Mahan, L. K., Raymond, J. L., & Escott-Stump, S. (2013). Krause’s Food & the Nutrition Care Process-E-Book. Elsevier Health Sciences. Available online at

(7) Parrish, C. R., Thompson, J. S., & DiBaise, J. K. (2016). Short Bowel Syndrome: Practical Approach to Management. CRC Press. Available online at

(8) Steele, S. R., Hull, T. L., Read, T. E., Saclarides, T. J., Senagore, A. J., & Whitlow, C. B. (Eds.). (2016). The ASCRS textbook of colon and rectal surgery. Springer. Available online at

(9) Feldman, M., Friedman, L. S., & Brandt, L. J. (2010). Sleisenger and fordtran’s gastrointestinal and liver disease E-Book: pathophysiology, diagnosis, management, expert consult premium edition-enhanced online features (Vol. 1). Elsevier Health Sciences. Available online at

(10) O’Brien, B., & Floruta, C. V. Management of a Peristomal Ulcer Using a Calcium Alginate Dressing with a Sacral-Shaped Transparent Adhesive Dressing. Available online at

(11) Yassen, T. A., Dwikat, M. W., & Amer, M. Dietary Routine among Diabetic Patients in West Bank. Available online at

María Laura Márquez
13 October, 2018

Written by

María Laura Márquez, general doctor graduated from The University of Oriente in 2018, Venezuela. My interests in the world of medicine and science, are focused on surgery and its breakthroughs. Nowadays I practice my more:

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