If you apply a facial moisturizer with an SPF of 15 then add a facial sunscreen with an SPF of 30 and then apply a makeup with an SPF 15 what is the total SPF protection you are getting?

A. 15

B. 30

C. 60

D. 45

E. 70

The answer is B, the total SPF protection you are getting is 30. Unfortunately, layering sunscreens does not give added SPF protection. Applying two sunscreens with an SPF of 15 gives you a total SPF of 15, not 30. The SPF you end up with is only the SPF of the highest sunscreen that you applied.

Turns out you don’t need math at all.

Post written by Jeffrey Benabio, MD. You might also like these other skincare myths:

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Photo credit: Tread

When you cut yourself, the skin heals because healthy cells migrate out from the hair follicles and in from the edges of the wound to cover the entire surface of the injured area. When a cut dries out, a crusted scab forms. Scabs are dried collections of dead cells, blood clot, and white blood cells. This crusted debris actually hinders healing because it gets in the way of the skin cells migrating to cover the wound. Allowing a scab to form, then, actually slows healing and can worsen the scar.

The best treatment for a cut is to keep the wound clean and moist at all times. This can be done by washing gently once a day with soap and water or with a solution of 1/2 hydrogen peroxide, 1/2 water. Then apply a greasy ointment such as Vaseline or Aquaphor to seal moisture in and cover the wound with a band-aid. Antibiotic ointments can also be used, but they probaby cause more harm than good.

Keeping a cut or wound covered and moist and preventing a scab from forming will allow healthy cells to migrate in easily, thus allowing the wound to heal more quickly and minimizing the scar formed.

Sorry, Mom.

Post written by Jeffrey Benabio, MD. You might also like these other skincare myths:

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Photo credit: Belinda Hankins Miller

Antioxidants can help prevent wrinkles by soaking up harmful free radicals that damage your collagen.

Wrinkles result when collagen is damaged by ultraviolet radiation. Antioxidants, regardless of how potent they are, cannot alter existing collagen that is damaged. Antioxidants therefore do not treat existing wrinkles.

In terms of topical creams, only products that can cause growth of new collagen such as tretinoin (like Renova®, Retin-A®, and Tazorac®) can treat existing wrinkles.

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Photo: Jon Rawlinson, Flickr.com

It’s not their fault; it has been drilled into them by countless magazines, product ads, and television commercials. Vitamin C, pomegranate, resveratrol, coffeeberry: Eat them! Apply them to your face! Add them to your cereal! Surely soaking up bad free radicals must protect you against cancer, no?

Well, if you are standing right now, then I suggest you sit. I have bad news. There is little if any good data to show that taking antioxidant supplements protect you against against cancer. In fact, the best data seems to suggest just the opposite — it increases your risk for cancer. Are you sitting now?

A study last year published in the Journal of Nutrition found that women who took a vitamin C, vitamin E, beta-carotene, selenium, and zinc supplement (thats one mega antioxidant pill) developed skin cancer at a rate of 1.3%.

In contrast, the women who were not taking the supplement developed skin cancer at a rate of only 0.7%; this was significantly less.

In particular, the study found that the rate of melanoma was 0.3% in women on the antioxidant pills and 0.08% in women not taking the pills. Again, significantly higher in the women taking antioxidants.

This is not the first study to show an increased risk of cancer in patients taking antioxidant supplements. A large trial of smokers several years ago showed that those taking high does of vitamin A actually had increased risk of lung cancer compared to those not taking vitamin A. A different study showed that patients taking vitamin E had increased mortality as compared to those not taking vitamin E. Another study has shown that taking dietary supplements of antioxidants leads to increased risk of colon cancer. Several aggregated analyses (studies that look at all published studies together) have concluded that beta-carotene, vitamin A, and vitamin E all increase the risk of death, while vitamin C seems to have no effect either way.

How can this possibly be?

It is plausible that cancer cells are at increased risk of damage from oxidative stress compared to your normal, healthy cells. In other words, taking antioxidants might ironically be protecting your cancer cells, allowing them to survive more than anything else.

It is likely that because cancer develops from long term damage to your cells, as in the case of skin and lung cancer, that trying to limit damage for a relatively short period of time by taking antioxidants like vitamin E or vitamin A probably has little or no effect. It is analogous to a car that is already rusted when you apply a protective sealant to it. The damage has already been done. Just as the sealant is protecting the already rusted car, the antioxidant is protecting the already cancerous cells.

Here are some recommendations that have stood the test of time and clinical study in preventing cancer:

• Eat a diet high in fruits and vegetables every day (in contrast to supplements).
• Limit your intake of simple sugary carbohydrates such as white bread, chips, etc.
• Exercise every day and keep your weight down.
• Protect yourself from the sun with broad spectrum sunscreens and protective clothing.
• If you decide to take a daily supplement, the only vitamin that I recommend taking everyday is vitamin D. There is good evidence that vitamin D supplements can be protective against certain cancers. Taking 1,000 IU of vitamin D3 a day is the best way (much better than sun exposure) for elevating your vitamin D levels. More on this in a later post.

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They took three groups of teens for two weeks: one group didn’t exercise, one group exercised then took a shower right away, and one group exercised then waited four hours before they showered (insert requisite sweaty teen joke here). They found that there was no difference in acne among the three groups.

Thanks to Harvard and Stanford, we now know the truth — body sweat does not make your acne worse.

Short, R. et al. Pediatric Dermatology, Volume 25, Number 1, January/February 2008 , pp. 126-128(3)

The patch test showed he was 3+ positive (that’s very positive) for carba mix, compounds used in the manufacturing or rubber. “That’s impossible,” he said. “Why?” I asked. “Because I’ve worked in a tire store my whole life,” he replied.

It is a pervasive misconception that if you have been using a product like a lotion, or been in contact with something like rubber, or even taken a medication like aspirin for a long time that you cannot be allergic to it. That’s false. You can become allergic to it.

In order to be allergic to something, like rubber, you must have been exposed to it or to something very similar to it. You cannot be allergic to something you have never been exposed to. My patient was exposed to rubber without problem for years, but then suddenly his immune system targeted it, leading to his allergy. Although it is most common to develop an allergy to something that you have been exposed to recently, the allergy can develop after prolonged exposure.

The immune system is fantastically complex. It manages to determine what is foreign and harmful to you with almost flawless accuracy, but sometimes it gets it wrong. The times when it responds inappropriately to harmless chemicals in your environment is what keeps me in business.

Photo credit: Eric Castro

Despite threats such as these, the truth is our immune systems are incredibly effective at fighting off infection. Many of the medications we take to combat or prevent infections are unnecessary – antibiotics for a cold being the consummate example – and in some instances do more harm than good.

So it’s no surprise that many skin surgeons (including me) use plain Vaseline® (white petrolatum) or Aquaphor Healing Ointment® instead of topical antibiotics for their post-operative wound care.

Studies have shown that there is little difference between plain Vaseline and a topical antibiotic in preventing a wound infection. Your skin and immune system have worked on the problem of preventing infections for millions of years; they are quite good at it, especially if the wound is clean to begin with, as in surgery. In most of these instances you don’t need an antibiotic at all – the wound will heal well with or without it.

So why not use an antibiotic ointment “just in case”?

Because the two most commonly used topical antibiotics, bacitracin and neomycin, have a high risk of causing contact dermatitis. Contact dermatitis — a bright red, scaly, very itchy rash — is what you get, for example, when you are allergic to poison ivy or nickel. If you have ever had a case of contact dermatitis, then you know it can be quite impressive: weeping or crusted blisters that are very uncomfortable. In fact, most phone calls that we get from post-surgical patients who think they have an infected surgery site actually turn out to be an allergic reaction to the antibiotic ointment. It’s a classic case of doing more harm than good.

The next time you have a surgery on your skin, or even if you have a minor cut at home, clean it with plain soap and water and consider using Vaseline. It will save you money (and may save you a visit to your dermatologist to treat your new itchy rash).

Of course, there are exceptions. If you think you have an infected wound, then see your physician as soon as possible.

The only antibiotic that has been shown to reduce the concentration and the effectiveness of hormonal contraceptives (birth control pills) is rifampin. Rifampin is a rarely used antibiotic used to treat tuberculosis and methicillin resistant staphlococcus aureus (MRSA) infections.

Antibiotics commonly used for acne such as minocycline, doxycycline, tetracycline, and erythromycin have not been shown to reduce the effectiveness of oral contraceptives.

Hormones, specifically testosterone, are important contributors to acne; birth control pills can reduce the levels of testosterone in women. When combined with an antibiotic and a topical retinoid, they make a powerful triple threat to defeat acne.

As always, be safe (birth control pills do not protect against STDs) and please consult your physician if you have questions about any of your medications.

The reason for the long-held belief may be that dehydration of the body after death, and subsequent shrinking of soft tissue, can create the illusion of growth of hair and nails.

For this and other popular myths that apparently even doctors believe (not me of course), see this NYT piece.

After Plucking

You can’t catch a cold from going outside without a jacket, and hairs don’t grow back thicker after you pluck them. I swear.

In fact, repeatedly plucking hairs can scar the follicle, which over time can lead to permanent loss of that hair. It is actually a very inexpensive way to remove unwanted hairs.

Waxing, threading, and plucking hairs are essentially the same thing; the hairs usually will grow back (unless you perform this repeatedly over a long period of time).

Electrolysis and laser hair removal, in contrast, destroy the hair follicle. Most of these hairs will not grow back and repeated treatment will lead to permanent hair removal.

If you pluck your hairs:

1. Start with good, clean slanted or straight tweezers. Be sure the edges are sharp, not damaged.
2. Pluck in the direction that the hair grows.
3. Grab and pull the hair out in one quick motion.
4. Pluck only one hair at a time.
5. Repeat.
6. Repeat again.

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