Natasha Reyes, international aid worker, on a career dealing with disaster

I've got three younger brothers and I'm the typical big sister. In the Philippines, the extended family numbers in the hundreds, so I see myself as part of a huge family, with cousins, aunts, uncles, grand-aunts and grand-uncles. I grew up in the Visayas region, in the central Philippines. It's a bunch of islands and most summers I was on the beach, running wild with scores of cousins. My mum was a paediatrician and she wanted to train in dermatology, so we moved to Manila when I was eight years old. Even in Manila, it was a small-village atmosphere. Our neighbour was my grandmother's sister. And as soon as school was out, we'd go back to Visayas.

I always went to my mum's clinic and, being the only daughter, I was expected to follow in her footsteps. I did a bachelor's degree in psychology and then went to medical school in Manila. I started my training in dermatology. It was the easy option - to follow in my mum's footsteps, inherit her practice, have a nice clinic and wear high heels every day - but I realised it wasn't for me. A patient's skin would be red, itchy and dry and I would think, "You're not going to die." But because it was so visible, the patient would be very bothered by it. They would say that it's not getting better and I'd say, "Stop scratching." That wasn't something I wanted to do, so I switched to emergency medicine and I was like a fish to water.

In the 1990s, MSF (Médecins Sans Frontières) had projects in the Philippines - a street kids project in Manila, an HIV project in the south, they were there when Mount Pinatubo erupted - so I knew about them. When I finished my training, they didn't have any activities in the Philippines, but they had an office in Hong Kong. A friend started working with them - he had a mission in Kashmir and was hooked - so I tried it. It was my second mission that got me hooked. It was in Kenya at the end of 2007. They had just had their elections and there was a period of post-election violence; people just started hacking at each other. It was my first time in Africa. I was terrified arriving in Nairobi and there were still the remains of burnt-out cars on the side of the road. I had been working in a hospital where you have all your tools within reach and now everything was new, and I was completely out of my element. The first week I was dealing with the wounded and then I was in charge of providing health care for 12,000 displaced people - mostly women and children who were traumatised. I worked with very experienced people and learned from them. What I like about emergencies is that the impact is immediate - it's instant gratification.

Every mission is my favourite and my worst. Especially the long missions - you go through the full range of emotions and challenges. I was in Colombia for eight months. We had mobile clinics in small indigenous communities in conflict areas. We were on these lanchas, long native boats, that didn't have roofs, so we were out in the blazing sun or the pouring rain. Each trip lasted seven to 12 days and we started out eating fresh fruit but it was canned food by the end. In the farther-off places that weren't too established the river was used for everything. I would be in a bikini in the river shampooing my hair and a floating object would go past, so we had to teach the basics: "Do your number twos downstream, please." It was very physical, sleeping in a tent, packing and unpacking, and when the water was low, you had to carry the boats and gear down to the shore. I'd never been so fit in my life. I had no idea I could deal with those conditions.

One of the biggest gifts you can get from MSF is the friendships you make, because the work is so intense. We never work with armed guards - you have to rely on your identity as your protection. In the field, we usually have a vest or T-shirt with an MSF logo. In Colombia, we would do our clinics in schools and put the flag on the roof, so the helicopters would know. In 2009, I had just come home from Sudan and was waiting for a visa for my next mission when Typhoon Ketsana hit. I worked for a few weeks as a doctor in one of the mobile clinics on boats in the flooded areas. I've seen worse, but seeing it in your own country and having to do it in your own country is different.