Pillowcases get blamed for a surprising amount of skin trouble. Sometimes the habit matters. Often it becomes a convenient explanation for a much larger routine problem.
The realistic version
A pillowcase can collect oil, sweat, hair products, makeup residue, and skincare. If it is visibly dirty or irritating your skin through friction, changing it more regularly is sensible.
But a clean pillowcase is not a substitute for a routine that works. It will not cancel out aggressive cleansing, incompatible products, or sleeping in makeup.
Look at the pattern
If irritation appears in a consistent area that touches the fabric, the pillowcase may be worth investigating. If your whole face is changing after a new active or cleanser, the fabric is probably not the main story.
The bottom line
Keep your pillowcase clean, but do not turn it into the villain every time your skin changes. Good troubleshooting follows patterns, not internet folklore.