Worrisome describes a thing — a situation, a number, a symptom, a piece of news — that makes people anxious. It points at the cause of the feeling, never at the person having it. The suffix -some means 'causing this' or 'tending to this', the same as in troublesome and tiresome. Two things worth knowing. First, register: worrisome is more formal and more written than 'worrying', and it is much commoner in American English. British and Australian speakers usually say 'worrying'; in Taiwan, textbooks and news follow both, so you will meet both. Second, strength: worrisome is a measured word, the word of a doctor, an editorial, or a report. 'A worrisome trend', 'a worrisome drop in sales', 'the test results are worrisome'. It says there is real reason for concern, calmly — it is not panic. If you want the everyday spoken version, say 'that worries me' or 'that's worrying'. You will also see it, less often, describing a person who bothers others rather than one who feels bothered, but that use is rare today.