mysql ibdata1 file corrupted or increased unusually

Question

We are using MySQL 5.2 version all InnoDB tables.

I have observed that ibdata1 file got increased very unusually like occupied 500 GB in 2 days.

In last 6 months, it had taken only 6 GB though there were no inserts at all. I also deleted the ibdata1, ib_logfile0 and ib_logfile1 and restarted mysql.

It worked fine. but again after 6 months same issue, and the ibdata1 got increased to 550 GB. There are no errors found in error log file.

I would like to know what may be the reason in general ?