The products, also known as topical anesthetics, are available in over-the-counter and prescription forms.

Skin numbing products are used to desensitize nerve endings that lie near the surface of the skin, causing a numbness of the skin. These topical anesthetics contain anesthetic drugs such as lidocaine, tetracaine, benzocaine, and prilocaine in a cream, ointment, or gel. When applied to the skin surface, they can be absorbed into the blood stream and, if used improperly, may cause life-threatening side effects, such as irregular heartbeat, seizures, breathing difficulties, coma, or even death, the agency warns.

FDA has received reports of adverse events and deaths of two women who used topical anesthetics before laser hair removal. In February 2007, the FDA issued a Public Health Advisory — “Life-Threatening Side Effects with the Use of Skin Products containing Numbing Ingredients for Cosmetic Procedures,” to warn consumers about these products.

Patients for whom an over-the-counter or prescription topical anesthetic is recommended should consider using a topical anesthetic that contains the lowest amount possible of medication that will relieve your pain.

Also, health care professionals should determine whether adequate pain relief can be safely achieved with a topical anesthetic, or whether a different treatment would be more appropriate.

The FDA strongly advises consumers not to:

• Make heavy application of topical anesthetic products over large areas of skin;

• Use formulations that are stronger or more concentrated than necessary;

• Apply these products to irritated or broken skin;

• Wrap the treated skin with plastic wrap or other dressings; and

• Apply heat from a heating pad to skin treated with these products.

• When skin temperature increases, the amount of anesthetic reaching the blood stream is unpredictable and the risk of life-threatening side effects increases with greater amounts of lidocaine in the blood.

A recently published study in Radiology looked at women taking acetaminophen and ibuprofen by mouth versus applying lidocaine gel, a topical anesthetic, to the skin to decrease discomfort during mammogrophy. The lidocaine gel was applied to a wide skin surface area and then covered with plastic wrap. There were no serious or life-threatening side effects reported in the study, nor were any reported when FDA discussed the results with the doctor who performed the study.

The study results favored the use of lidocaine as there was significantly less discomfort than with the plain gel or oral acetaminophen or ibuprofen. However, given the life-threatening side effects associated with the use of topical anesthetics during laser hair removal, FDA is concerned that similar side effects could occur when topical anesthetics are used during mammography. Further, the study was small and it is possible that a larger study might show different findings.

Patients should talk with their health care professional if they are considering using a topical anesthetic before a mammogram. The following summarizes advice for patients if a topical anesthetic is recommended for their use:

• Use a topical anesthetic that contains the lowest strength, and amount, of medication that will relieve the pain;

• Apply the topical anesthetic sparingly and only to the area where pain exists or is expected to occur;

• Do not apply the topical anesthetic to broken or irritated skin;

• Ask their healthcare profesional what side effects are possible and how to lower their chance of having life-threatening side effects from anesthetic drugs; and

• Be aware that wrapping or covering the skin treated with topical anesthetics with any type of material or dressing can increase the chance of serious side effects, as can applying heat to the treated area while the medication is still present.