By far the most common allergy, and also the allergy that might easily develop or worsen from playing the bass guitar is nickel allergy. Less common, but also to beware of are chrome allergy and brass allergy, with similar symptoms. Nickel allergy is a contact allergy, caused by skin contact with objects containing nickel. Sweat will dissolve tiny particles of nickel oxide on the object’s surface. This solution, if absorbed by the skin, may cause various skin problems. Find detailed info here. Also I suffered severely from this nasty allergy, so I am an expert from personal experience.
Take notice of the fact that nickel allergy often builds up slowly and unnoticed. You may play nickel wound strings and enjoy their warm sound for years without problems, and then, suddenly, the allergy breaks out. First step is to see a dermatologist to be sure it ís nickel allergy you are dealing with. Secondly, avoid contact with all objects that may contain nickel. Those are quite a few: keys, coins, tools, jewelry etc. etc. Nickel allergy is a good reason to be suspicious of all small metal objects. Not necessarily cheap objects, since for example white gold contains nickel also.
Most bass guitar strings are made of alloys containing nickel. Even strings wound with steel, chrome or bronze may contain nickel. Try to get correct info from your manufacturer. That will not be easy.
In my opinion, strings manufacturers should mention the allergenic risks of their product.
Problems may also be caused by other metal parts of the bass, like frets, tuners, pots, switches, bridges or pickup covers.
Important precautions:
The hard skin on your fingertips will not easily absorb nickel oxide, but tender areas like the sides of the fingers and the skin between the fingers are more vulnerable. The nickel oxide causing the allergy may well spread all over your hand long after playing. So wash up!
For bass players already suffering from nickel allergy, it is not always clear which contact caused the latest outbreak. Problems may arise up to a few days later. This means you are forced to take all precautions possible.
Avoid all contact with objects that may contain nickel. That will not be easy, since nickel is everywhere. Do not touch or wear nickel objects. Replace them with hypoallergenic stuff, like a special watch band, a plastic covered key ring etc. In very serious cases, wearing cotton gloves may be needed.
For bass players struck by nickel allergy, I recommend coated or nylon wound strings. Clear lacquer, paint or tape may shield off all metal parts that are frequently touched during play. Take notice of the fact that coatings on metal parts wear off, again allowing your skin to get into contact with the bare metal. If you decide to buy new parts or a new instrument, try to find out which metals the hardware is made of. Fancy hardware may be gold or silver plated, but in most cases, plating will be very, very thin, wearing off soon at the rims or places touched frequently.
Hypoallergenic fret wire already is available. Plastic and wooden pot knobs are on the market. The waiting is for a company that offers complete hypoallergenic and versatile hardware sets for common types of bass guitars.