When to Use Topical Antibiotics

Walk through the aisles of your local pharmacy, and you'll notice an array of over-the-counter antibiotics in the form of creams, salves, and ointments (think Neosporin and Polysporin). However, just because you can freely purchase these products and apply them ad libitum doesn't mean that they work well. Furthermore, the improper use of topical antibiotics can pose a public health hazard in the form of increased antibiotic resistance. Overall, topical antibiotics have very few appropriate (evidence-based) uses.

Acne

When used to treat acne, topical antibiotics shouldn't be used as sole treatment (monotherapy) for more than 3 months. 

Mild to moderate acne can be treated with topical antibiotics like clindamycin, erythromycin, and tetracycline in addition to benzoyl peroxide. When used in combination. benzoyl peroxide and topical antibiotics reduce the risk that resistant strains of Propionibacterium acnes (P. acnes) will emerge. Of note, P. acnes is a slow-growing, gram-positive bacteria that contribute to the development of acne.  

Clindamycin is probably more effective than erythromycin when treating acne long-term. Furthermore, clindamycin has been linked to decreases in the number of blackheads (comedones and microcomedones) typical of acne. In addition to being combined with benzoyl peroxide, clindamycin can also be combined with tretinoin for the treatment of acne.

Another topical antibiotic that can be used to treat acne either alone or in combination with other drugs is dapsone. Interestingly, dapsone was originally used to treat people with leprosy when physicians noticed that it also reduced acne. Unlike oral dapsone that can cause potentially fatal hemolytic anemia in people with G6PD deficiency; however, topical dapsone is safe because it isn't absorbed into the blood.

On a related note, when used to treat acne, some topical antibiotics not only fight bacterial infection but also reduce swelling.

Wounds

In the 1960s and 1970s, physicians discovered that the application of topical antibiotics to surgical wounds dramatically decreased the risk of infection. Furthermore, the moist environment in part established by the application of topical antibiotics promoted healing. More recently, less evidence suggests that topical antibiotics prevent infection in wounds. Nevertheless, many pharmacies still sell topical antibiotics with the promise that they help fight infection.

For at least two reasons, the use of topical antibiotics can be unsafe. First, topical antibiotics and other antibiotics used with wound care contribute to the emergence of antibiotic-resistant bacteria, most notably MRSA. Second, people often develop an allergy to topical antibiotics like neomycin and bacitracin. These allergic reactions appear as dermatitis or skin inflammation and can be aggravated by continued application of topical antibiotics, which often happens with wound care.

The decision whether to use topical antibiotics for wound care should best be left to your physician. Ultimately, topical antibiotics probably help only a small subset of patients with wounds like those who are immunocompromised or have diabetes. Moreover, with most minor surgical wounds — wounds created during an aseptic procedure like skin biopsy — topical antibiotics are probably unneeded.

Impetigo

Impetigo is a common skin or soft tissue infection usually caused by a staph or strep bacteria. In the 1980s and 1990s, the topical antibiotic mupirocin was considered better than neomycin or polymyxin at treating impetigo. Nowadays, because of the rise of MRSA and other types of antibiotic-resistant bacteria, mupirocin is ineffective in many cases of impetigo. In fact, if you have a skin or soft tissue infection, your physician will most likely prescribe you an oral antibiotic like Keflex (cephalexin) or Trimethoprim-Sulfamethoxazole (TMP-SMX) which is active against MRSA. 

In conclusion, topical antibiotics have very limited medical uses. At best, when you purchase topical antibiotics for self-treatment, you're likely wasting your money. At worst, you're contributing to antibiotic resistance and skin allergy.