Infections can be fairly mild, like a rash with blisters, or they can become severe abscesses requiring surgery and months of antibiotics to cure.

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The eighth seed retired early in the second set with blisters to keep Roddick's hopes of a first title this year alive ahead of next week's French Open.

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Now he lies in Kandahar's main hospital, his face swollen with black blisters.

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As with chickenpox, the blisters turn into crusty scabs before healing after about a week or two.

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Within a day or two, many of these lesions turn into small blisters filled with clear fluid, which then turns into pus.

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The blisters, each with its own bar code, move to a collating table and are rearranged in a pattern before getting bagged.

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An estimated 16% of U.S. adults are infected with herpes simplex virus type 2 (HSV-2), which can cause bumps, blisters, or sores on the genitals and surrounding areas, along with pain and itching.

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Blisters on Nadal's right foot provided Nieminen with some unlikely hope but the second seed, who was on court for the fourth successive day, recovered and broke in the fourth game when a resigned Nieminen netted a backhand.

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The world number two, who had won all four of his previous encounters with Almagro without dropping a set, has endured a torrid time with injuries in the last few months and was troubled by blisters to his feet in the duel, which lasted three hours 14 minutes.

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The blisters, by the way, are a hangover from the streets of Brussels and nothing to do with the trainers, which are as comfortable as a glove on a cold day.

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