A cast is a rigid support used to immobilize a fractured or injured bone, allowing the tissues to heal in the correct position. This protective shell is only effective if it maintains its original shape and integrity, which is why the universal instruction from healthcare providers is to keep the cast completely dry. Water is detrimental to a cast regardless of whether it is made of traditional plaster or modern fiberglass, and moisture can quickly lead to both structural failure and dermatological complications.
How Water Compromises Cast Structure
The immediate effect of water exposure depends heavily on the material, but the outcome is always a compromised supportive function. Plaster casts, made from a plaster-of-Paris mixture, lose their rigidity almost instantly when exposed to water. The plaster reacts with the water, causing it to soften, crumble, and dissolve, destroying the cast’s ability to hold the bone still. This structural failure means the fractured limb is no longer properly immobilized, which can hinder the healing process or expose the injury to the risk of re-displacement.
Fiberglass casts, while more water-resistant on the exterior shell, fail internally when the padding gets wet. The soft, absorbent lining material acts like a sponge. Once this padding is saturated, it swells, compresses, and then retains the moisture, leading to a loss of the precise fit required for effective immobilization. A softened or compressed lining can also shift, creating pressure points that can cause skin injury or allow the limb to move within the cast, undermining the intended therapeutic support.
Risks to Skin and Limb Health
The retained moisture within the cast creates a dark, warm, and humid environment that poses risks to the underlying skin and limb health. Skin maceration is the most common consequence, where the skin becomes soft, wrinkled, and weak, similar to skin after prolonged time in a bath. This oversaturated state breaks down the skin’s natural protective barrier, making it highly susceptible to injury and infection.
The trapped dampness is a breeding ground for microorganisms, leading to the rapid growth of bacteria and fungi. This microbial overgrowth often results in severe odor and intense itching. Scratching can break the already compromised skin, and combined with the moist environment, this can quickly escalate into a serious skin infection, such as cellulitis, which requires immediate medical intervention. For patients with surgical incisions or pins beneath the cast, a wet cast increases the risk of a deep wound infection, which can complicate recovery.
Immediate Action Plan
If a cast gets wet, immediately assess the extent of the saturation. If the cast is merely damp, or only a small area of the padding is wet, attempts at safe, at-home drying can be made.
At-Home Drying
The safest and most effective method is to use a hairdryer set to the cool setting, aiming the air into the ends or openings of the cast. This cool air helps to circulate and evaporate the moisture from the inner padding without damaging the cast material or burning the skin. Avoid using the hot setting on a hairdryer, as concentrated heat can cause severe thermal burns to the skin under the cast. Never insert any objects, such as towels or rulers, into the cast to dry the padding or scratch the skin, as this can push debris against the skin or cause injury.
When to Seek Medical Attention
If the cast is completely saturated, or if the padding still feels wet after 24 hours of consistent cool-air drying, professional help is necessary. Seek immediate medical attention if you notice any of the following symptoms:
- A foul odor
- Drainage
- Fever
- Persistent or increased pain
- A feeling of tightness
- Numbness or tingling
- The cast visibly softens or changes shape