Now, before we start bashing Hot Topic for having lead in their jewelry, keep in mind that at least they're being honest. Under penalty of law. There are plenty of other shops online that don't have to reveal this. It probably cuts into sales.
Lead isn't the only dangerous metal used in cheap jewelry, though it's the most dangerous. And it's absorbed through the skin. The other hazardous metals, as stated by OSHA (Occupational Safety and Health Administration) are arsenic, beryllium, cadmium, hexavalent chromium, lead, mercury. I don't think I need to tell you how dangerous these are. They are used as a filler for more expensive metals (which is why cheap jewelry is cheap). It isn't illegal to sell toxic jewelry for adults, by the way. For children, yes, but not for adults.
These are the metals we should be worried about. But, having worked at a jewelry store, everyone was terrified about nickel. 10-20 % of people are allergic to nickel (dermatitis). Longtime exposure causes it anyway. (source). Before you take a look at the material safety data sheet (MSDS), know that MSDSs cover all forms of it--including dusts and powers. You aren't going to get lung cancer from a toe ring. In fact, according to this government report about nickel causing cancer, most people consume nickel through food and water. If you are interested, there are MSDS for all of the metals. Search away. The state of it matters. So when you are looking at MSDS, look for your metal in solid, metal form. Not in dust, soluble, or salt form. and obviously don't go eating your jewelry.
So, compared to the toxic metals that are actually banned from OSHA above, nickel isn't so bad. The only confirmed issue through skin contact is dermatitis. White gold is 10% nickel, by the way, unless it's mixed with platinum. Some metals, like copper and gold, have been shown to be safe and are used in dental fillings and plumbing for drinking water.
I, personally, am allergic to all metals except brass (an alloy of copper and zinc), titanium, and surgical stainless steel. I'm also allergic to chemicals, the sun, everything. Eczema, dermatitis all the time. right now, the entire side of my body is covered in red scales for no reason. This is why I don't usually wear jewelry or only wear jewelry made of woods (which aren't always safe...I guess another post for those), horn, bone, leather, cloth, or glass.
Basically, any metal that you put into an open wound--aka implant-grade surgical steel--shouldn't cause a reaction. Here's a useful picture detailing the difference between implant-grade and regular surgical steel. Porous metals harbor bacteria, as you know.
My only advice for wearing questionable metals or metals that irritate you is to not wear them against your skin. Turtlenecks, collared shirts.
You can't tell if your cheap $5 necklace you bought at the mall has toxic chemicals unless you've got a laboratory. An etsy person who hand-assembles jewelry from store-bought items isn't getting MSDS from the manufacturers of those chains and clasps. Good shops will tell you what metal your item is.
A good indicator is price. Pure metals are expensive. But a seller could jack up the price of cheap metals just as easily if there's a demand for it.
Sorry to rain on everyone's parade.