Meaning of "Over" in this sentence

Question

A standardised “60 second hair count” is regarded as a reliable method of assessing hair shedding How to do the hair count: wash your hair over 3 days. On the 4th day, comb your hair forwards for 60 seconds over a contrasting colour towel or pillowcase before shampooing then count the hair loss for three consecutive days usually only about 10 hairs on average are lost per day in normal healthy males, regardless of whether you’re young or middle-aged the test can be repeated on a monthly basis to keep a check on your hair health

Which means washing hair for 3 days ? or not washing hair for 3 days ? I lost about 20~30 hairs two days after I washed my hair last time. According to the above contents, is it hair loss disease ?

Answer 1

From a related article, Standardizing the 60-Second Hair Count :

The subjects used a shampoo (...) once daily for 3 consecutive days in the morning. On the fourth day, they were instructed to comb their hair for 60 seconds before shampooing in the morning, starting at the vertex and combing forward. The hair was combed over a towel or pillowcase of contrasting color so that any shed hairs could be adequately visualized. The subjects then collected the shed hairs and recorded their number. This “comb-and-count” technique was repeated on 3 consecutive days.

The quote you provided which said "over 3 days" almost certainly meant "once daily for 3 consecutive days in the morning."

If you do something "over the course of three days", that could be abbreviated to "over three days". It indicates the activity will take that period of time, without necessarily implying that you will spend all your time doing it. However, it usually implies you will somehow spend a non-trivial amount of time during those three days.

Using that to describe "washing your hair" is not the best choice. They have maximally abbreviated their idea, condensing it down to only three words: "over three days". If you analyze the paragraph, it can only have one reasonable interpretation, so from this perspective it basically makes sense. But in my opinion, they have over-abbreviated, and it would be clearer to use the longer more scientific explanation.