Can an IV line cause bruising or infection?

Yes, it can, and the useful part of the answer is how likely each outcome is. Bruising and infection are not the same size of risk.

What the risk looks like

AARP states the risk this way. Because you are getting a needle placed in your arm, there is a chance of pain or bruising or, in rare cases, infection or inflammation of the vein.

The sentence is ordered by likelihood. Pain and bruising come first and are the more likely events. Infection and inflammation of the vein are described as rare. Both belong in your decision, but they should not be weighed as equals.

In the days before the first needle

It usually comes up in the days before a first appointment, when the idea of a drip has become real and the needle has not. The AARP article on whether IV vitamin therapy works and the Harvard Health piece asking whether IV vitamin therapy is a health boost or an expensive placebo frame the larger question of whether the drip is worth any risk at all.

Watching the arm after the visit

After the appointment, watch the arm where the line was placed and note anything that changes.

When the site does not settle

If the site gets worse instead of better, contact the provider who placed the line and describe what you see. Do not decide for yourself that it is only a bruise.