Dear Dr. Ken: I got a new tattoo a few days ago and it has been itching. My other tattoos never bothered me at all. Is this in my head or could the tattoo actually be making me itch? -- Keith G.

Dear Keith: Forty percent of people aged 18 to 40 have one or more tattoos, according to some estimates. Given how common tattoos and piercings have become, there's relatively little data on their health effects. Here are some major concerns and what to do about them.

Skin reactions: Itching, redness and rashes are fairly common. The inks used, despite being injected into your skin, are not regulated or tested for safety in the same way the government tests food, cosmetics and medicines. Meanwhile, analysis of inks used in tattooing have been shown to include metals such as aluminum and cobalt as well as others which can potentially cause allergic reactions such as redness, irritation and itching. (California is the only state that requires ink manufacturers to provide a list of ink ingredients.)

Itch Treatment: Over-the-counter medicines such as calamine lotion and/or corticosteroid cream will, in most cases, make symptoms go away within seven days. If symptoms are at all severe or are mild but last more than a week, see a doctor. If a piercing is the issue, remove it. Once gone, trying again with a less troublesome, although pricier, jewelry of sterling silver or solid gold may resolve the problem.

Read more about bleeding and infection concerns after the jump.

Bleeding from Piercings: Usually, the bleeding is minimal and stops on its own. One study found that while tongue piercings are the most likely to bleed, bleeding from genital piercings is the likeliest reason for seeking medical attention (and the most understandable).

How Do You Know If It's Infected? Infections are usually a result of the tattoo artist not following proper sterile technique or the customer not following proper after-care practices, and typically make themselves known with pain, redness, swelling and/or pus. Severity of infections can run the gamut from no big deal to very big deal. In many cases, it isn't obvious where on that spectrum an infection may fall so it's best to let a health professional make the call. One obvious warning sign is fever, which likely means the situation is serious. When deemed necessary by a doctor, antibiotics will often do the trick.

A Little Red: For very mild cases, elevation and soaking the area with warm compresses may take care of it. Getting some antibiotics from your doctor may also be a good idea.

'Staph' Infections: These drug-resistant bacteria strains are increasingly common everywhere, including among those with tattoos and piercings (Community Acquired Methicillin Resistant Staphylococcus 'Staph' Aureus or CA-MRSA). More serious infections -- including those of the heart, blood and kidneys -- have been seen in rare cases. Because these infections are more serious, they require treatment and monitoring by a doctor.

The Big Three Infections: Hepatitis B, Hepatitis C and HIV. For Hepatitis, cases have occurred rarely so the risk is real, but just how great a risk isn't clear. HIV transmission on the other hand, is theoretically possible but no cases of infection through piercing or tattooing have been documented.

What You Can Do: Make sure the environment is sterile. The person giving you the tattoo should, for example, use new sterile needles and disposable gloves. The skin site should be cleaned with antimicrobials such as iodine- and/or alcohol based solutions.

As gifted as tattoo artists often are, no formal training is required (though some states do have examinations) so safe practices can vary widely. A common sense approach would include going to an experienced, reputable, commercial artist where clean conditions and sterile equipment are available.

Dr. Ken Spaeth is a Harvard-trained physician and a faculty member at Mount Sinai School of Medicine in New York . He is also co-author of "The Bioterrorism Sourcebook." You can e-mail him your questions at askdrken@aol.com.