Is it bad to use 'um' and 'uh' when speaking English?
No. They are ordinary English words, used by native speakers in every conversation, and the research treats them as signals rather than errors. What costs you is repetition: the same sound in every sentence, or one that runs for two seconds while you search.
No. They are ordinary English words, used by native speakers in every conversation, and the research treats them as signals rather than errors. What costs you is repetition: the same sound in every sentence, or one that runs for two seconds while you search. In an interview or a speaking test a filler is much cheaper than silence, because silence reads as a lost turn.
One research detail is worth knowing when you choose between them. In the 2002 study the two sounds contrasted mainly in the length of the delay that followed: um preceded longer pauses than uh. That makes uh the cheaper sound for a word you are about to find, and um the one to keep for a change of direction or a longer search.