As published in the May 1961 issue of Good Housekeeping...
Of the many laundering problems that come may way, the most baffling are tiny holes in cotton clothing, sheets, pillowcases, and other items. They're usually notices soon after laundering and most often appear in white rather than in colored goods. When a number of pieces are affected, the matter is understandably distressing!
The Good Housekeeping Institute laundry laboratories have studied this problem through the years as readers have reported it. By examining representative damaged articles and by chemical tests and other means of laboratory detection, we've searched for the answer. While even with laboratory equipment it is difficult -- sometimes impossible -- to pinpoint the exact cause, there are several possibilities that merit exploration by any homemaker who discovers mysterious holes in a wash load.
The specifics are contained in the scan below, but note that the big three reasons listed are bleach, the washer and dryer, and "the great unknown".