Some people have used to use the same silk sheet for long time and often wash them once a week or two weeks. It is not helpful to make silk sheets last longer.
The frequent wash of silk bedding sets will fade quicker. The right method is to use them alternatively. Silk can evaporate your sweat very quickly and most bed allergens can’t survive in silk. So it’s going to stay much cleaner, much longer. It is recommended that you wash them every 2 or 3 weeks.
As for the alternative use of sheets, it doesn’t mean that you have to use silk bed covers. Other sheets that are made of different materials are also acceptable.