Should you cover a cut or let it breathe?
Cover it. The advice to let wounds "breathe" and form a hard scab is widely repeated and contradicted by decades of wound healing research.
Why covering works better. The key concept is moist wound healing, established by George Winter's research in the 1960s. Winter demonstrated that wounds kept moist under a covering epithelialised roughly twice as fast as those left to dry and scab.
The reason is straightforward once stated. New skin cells must migrate across the wound surface to close it. In a moist environment they move freely across the surface. Under a dry scab they must burrow underneath it, through dried tissue — slower, and requiring more energy. A scab is an obstacle to healing, not a protective achievement.
Moist healing also produces better cosmetic results, with less scarring, and is generally less painful.
The other benefits of covering: protection from bacteria and contamination, protection from mechanical knocks and reopening, and retention of the natural wound fluid containing growth factors and immune cells.
How to do it for a minor wound: clean under running water, avoid harsh antiseptics on the wound bed since they damage healing tissue, dry the surrounding skin, and apply a plaster or dressing. Change it when wet, dirty or daily, and allow the skin around it to stay dry. Hydrocolloid dressings maintain moisture particularly well.
The distinction that matters is moist versus macerated. Sealing a wound so it sits in fluid causes the surrounding skin to go white and soft, which is unhelpful. A breathable dressing appropriate to the amount of fluid is the aim.
When to seek medical care: deep wounds, anything gaping that may need closure, bites, puncture wounds, wounds with embedded material, signs of infection — spreading redness, increasing pain, warmth, pus, fever — and any wound in someone with diabetes or poor circulation.
Check tetanus status for dirty wounds.