In 2004, law student Daniel Tan, who was doing his national service, started feeling some pain in his right big toe.

Examining it, he found it swollen and producing pus. His toenail was digging into the flesh surrounding it, probably because he had trimmed the nail too deep.

"It hurt and annoyed me," he said.

Over the next two weeks, he clipped the nail regularly to keep it from cutting further into the flesh and used an antiseptic cream to keep the swelling down.

Luckily for him, the problem went away.

"I didn't think of seeing a doctor at the time but it was very painful and troublesome to have to keep trimming the nail," said Mr Tan, 27.

He was suffering from an ingrown nail or onychocryptosis, the medical term for it.

This is a form of nail disease in which the growing nail cuts into either side of the nail bed. Although it can occur in hands and feet, it most commonly affects the toenails.

Ingrown nails can be caused by ill-fitting shoes and trauma to either the toe or toenail, such as injury when playing sports like soccer.

This can cause the nail to grow irregularly and dig into the surrounding flesh. Most often, it affects the big toes as they are most prone to injury.

Not cutting one's nails properly is also a common reason behind ingrown nails, said Ms Kin Ismail, senior podiatrist at the Singapore Footcare Centre.

"People like to cut the nail on their big toe deep and then try to clean away the debris around it," she said.

This can often leave behind spiky portions of the nail that will start irritating the area around it.

When the skin is pierced, granulated tissue can start forming around the spot - a process called hypergranulation - causing pain and making the area very sensitive to pressure.

Left untreated, infections can easily occur, leading to swelling and even pus.

In the case of those with conditions affecting their blood flow, like those with diabetes, such infections can even lead to gangrene, Ms Kin said.

She added that most attempts to trim ingrown nails on one's own do not really work as it is hard for most people, especially the elderly, to properly reach and manipulate their toes.

She recalled one female patient who ended up stabbing her toe with a nail cutter while trying to tend to the affected nail area.

"This just made it worse as the toe was already red and angry."

In mild cases, treatment involves using a special set of clippers to trim the nail's sides so as to remove the offending spiky areas. Antiseptic creams can also be used to deal with swellings and infections.

For those who repeatedly suffer from the condition, nail surgery can be performed to permanently remove the affected portion.

Using a local anaesthetic, the affected portion of the nail is trimmed down to the cuticle, following which phenol (a type of caustic agent) is applied to stop the nail's irregular growth.

Ms Kin said that this treatment is successful in 93 per cent of cases to deal permanently with ingrown nails.

Another option is to have the nail entirely removed, said family physician Kelvin Phua.

This procedure, called nail avulsion, can be done quickly using local anaesthetic and a pair of surgical pliers. Some oral antibiotics may be prescribed to fight any infections present.

Removing the nail, he added, will allow the area some rest and give a chance for the nail to regrow properly.

The best way to prevent ingrown nails is to trim them properly.

Instead of cutting toe nails deep and following the curve of the nails, cut them straight across, he said.

This article was first published in Mind Your Body, The Straits Times, on January 1, 2009.