Does anyone know what the outside of the harmonica is made out of. I thought steel or aluminum but I'm not sure. By the way, if anyone knows specifically for the Johnson harmonica, that would be great.

In general, most harmonica covers are made of steel that has been plated, usually with nickel. Some have a painted coating (such as the Bushman Soul's Voice and the Hohner Pro-Harp and Cross Harp) instead of nickel to reduce irritation, and provide a smoother feel, and some (usually your cheaper ones) might be made of aluminum or plastic. Unfortunately, I don't know what your Johnson harmonica is made of.

Thanks, because I need some sort of alternative because the nickel seems to be irritating and swelling my lips and I'm not sure why since I've played this same harmonica for about a year now.

First question: Have you had any reactions to nickel or other metals in the past?

If the answer to that question is, "No," the next question is: Have you recently gotten any piercings or had any changes in diet?

The reason is, that it is possible to develop metal allergies from having your ears pierced. Also, increases in certain food (especially those that have high acid content) can cause reactions with certain metals.

If the answer to that question is also no, then I'm out of ideas.

A lot of people are allergic to nickel. Nickel is used in a lot of materials and in low percentages even people who are allergic won’t have a reaction. The original Euro design had a very large percentage of Nickel in it. The result was a large amount of people began having reactions to the currency so they lowered the Nickel percentage to correct the problem. I would think that in the harmonica they would use a low percentage of Nickel to avoid reactions. Are you keeping your lips moist? It could be that your lips are just getting raw from playing and swelling. I had that problem when I was learning to play.

Allergic reactions can be funny sometimes. Even though you have an allergy to something you may not have a noticeable reaction when you are at first in contact with it. The reaction then occurs seemingly out of the blue. Normally there are triggers like the ones mentioned by pcguyiv. Finally people can develop reactions to materials after continued exposure to them.

Well I haven't ever had any piercings and I don't believe my diet has changed much. I may have to work on keeping my lips a bit more dry because over the summer, they have become very dry and chapped. If I am allergic to the nickel, would I need to get a new harmonica?

A new harp isn't necessarily necessary. There are many remedies from using clear fingernail polish to buying plastic covers. One suggestion is to keep some vaseline or carmex on hand to keep your lips from chapping. If your allergy is extreme, then, yes, you probably would need to buy a new harp.

If you decide on a new harp, your best options are (in my personal order of preference):

#1: Bushman Soul's Voice
#2: Hohner Pro-Harp
#3: Hohner Cross Harp

There may be others, but those are the easiest for me to think of.

The reason I'd say the Soul's Voice first is because it also has completely recessed reed plates, so you don't have to worry about reaction to the brass either.

Could chrome be used as a substitute for nickel because I found some chrome-plated harmonicas. Are all steel harmonicas plated with nickel because I found some that said they had stainless steel covers but never mentioned nickel.

As far as the ones that say they are stainless steel, they don't have any kind of plating on them, but they can still leave a rashy feeling, though not as bad as some of the plated ones.

Unfortunately there are some chrome platings out there that still have nickel in them as well as chromium. In fact, some "chrome" finishes are merely polished nickel rather than real chrome.

While there isn't anyone allergic to iron, it is still possible to be allergic to chromium, though it is rather rare. This is why stainless steel (which is basically iron and chromium-oxide) is considered hypo-allergenic rather than non-allergenic.