Tattoos are all the rage these days. And many young people sport them - from the small and discreet, maybe even hidden - to the tattoos that grow and grow - or what's termed extreme tattoos.

They all draw attention.

But do they also spark a reaction inside the body?

They are, after all, a series of deep, puncture wounds filled with ink pigments injected via needle pricks into the middle layer of the skin called the dermis.

Dr Eileen Tan, consultant dermatologist at Eileen Tan Skin, Laser and Hair Transplant Clinic at Mount Elizabeth Medical Centre, said: 'What makes tattoos so long-lasting is that they're so deep. Dermis cells are very stable so the tattoo is practically permanent.'

When tattoo ink pigments are introduced into the skin, the body reacts to such foreign particles by trying to remove them.

The pigments, now engulfed by white blood cells, will sink deeper into the dermis over time. Some are drained away from the skin into the lymph nodes, causing tattoos to fade or their margins to become blurred.

While there is no limit to the length of time or amount of skin given over to a tattoo, tattoo artists advise a maximum of four hours.

Mr Alecs Khoo, 35, owner of tattoo studio Alive Tattoo, said: 'After four hours, a person may go into shock. His skin may become too swollen and his body may start rejecting the ink.'

He added that going beyond your own endurance limit may cause the skin to scab more during the healing period. Some customers even break out in fever after an extended tattoo session.

Mr Joseph Siow, 30, owner of tattoo studio Visual Orgasm, added: 'Even if someone can take the pain, his skin will become so swollen that the ink won't go in. Once skin swells, it's hard for us to do our work.'

The skin's 'healing period' from a fresh tattoo varies in individuals, from three days to even a month.

Ms Rebekah Kong, a diabetic whose right half of her body is emblazoned with peony and koi tattoos, said her skin usually takes 10 days to heal and she is sensitive only to red tattoo ink.

Although she was advised by her doctor against getting tattoos, she went ahead anyway to prove that her condition was not a handicap.

Besides diabetics, doctors also discourage pregnant women, people with risk of keloid formations or skin diseases as well as people whose immune systems are weak or compromised from sporting tattoos.

A botched tattoo job does not just mean a ruined patch of skin, marred by uneven texture, raised skin or unattractive colouring. It can also lead to blood-borne diseases like HIV or Hepatitis C, skin disorders, bacterial infections in the skin which cause swelling and pus and itchy rashes due to allergic reactions.

Dr Yeap Choong Lieng, consultant plastic and cosmetic surgeon at Yeap Plastic Reconstructive and Cosmetic Surgery, cautioned: 'The threat of transmittable diseases like Hepatitis B, C, HIV and others can be real in a non-sterile environment where needles are re-used and not sterilised.'

Tattoo artists here are not required to obtain a licence before setting up practice and there is no regulatory authority for tattoo studios.

But the tattoo artists who spoke to Mind Your Body said that for them it is standard practice to sterilise equipment in an autoclave machine and use new needles for each tattoo session.

Some tattoo enthusiasts, like make-up artist Candy Wong, 26, are less worried about infection than design prices. She got a palm-sized tattoo of a red rose on her back in Bangkok in 2004 for less than $80.

A smaller, simple tattoo can cost $50 and upwards in Singapore.

Ms Wong said: 'I didn't worry because it looked pretty respectable. I spoke to the tattoo artist beforehand and felt I could trust him. And he showed me the new needle he was going to use.'

While the risks of infection and contamination are mitigated by tattoo artists ensuring hygiene standards, there are still safety concerns over tattoo ink.

The Food and Drug Administration in the United States has not approved any tattoo ink pigments for injection into the skin and stated in a consumer update last December that many ink pigments used are industrial strength colours suitable for automobile paint or printer ink.

In 2005, Arsenal footballer Fredrik Ljungberg famously suffered from an inflamed hip due to an allergic reaction to the ink in his two tattoos. He eventually had an operation to remove an inflamed lymphatic gland.

Five doctors Mind Your Body spoke to said that tattoo pigments do not cause any bodily problems when left in the skin in the long term.

Dr Chua Sze Hon, senior consultant dermatologist at the National Skin Centre, said: 'Generally, tattoo pigments are inert and not harmful if obtained from established sources.'

The problem for most people is a tattoo's permanence - when they have outgrown it, due to age or a change in personal circumstances.

Each year, the National Skin Centre sees between 100 and 200 new patients who want their tattoos removed. This is done via a special pigment laser procedure which starts from $200 for a small area of skin. Multiple treatments (between seven and 10) are often needed to remove professional tattoos.

Sales assistant Nur Shazlina, 18, who is getting two tattoos on her wrist and back removed, said: 'I got them when I was 12 years old. When people see my tattoos, they think I'm not a decent, normal girl.

'When I was younger I followed my friends who said it was cool to have tattoos. I've grown out of that.'

junec@sph.com.sg

A person being tattooed may go into shock after 4hrs with his skin becoming too swollen to acccept the ink

' The threat of transmittable diseases like Hepatitis B, C, HIV and others can be real in a non-sterile environment where needles are re-used and not sterilised.'

Dr Yeap Choong Lieng

This story was first published in Mind Your Body, The Straits Times, on May 7, 2008.