It's summer time and the living is easy - right? The temperature nudges upwards and gradually we feel more relaxed. The sun comes out and the rays help strengthen our bones, they even whiten our teeth. But with all the positive effects of summer come a host of negative ones. From allergies to stomach bugs and the headline-grabbing 'economy-class syndrome', the holiday period isn't always a (gentle) breeze. Here's the latest research to ensure a happy, healthy summer 2001.

1. Sunscreen needs to be absorbed into the skin for it to work. If you apply it on the beach, you'll be sitting there for 20 minutes unprotected, which is enough to burn. You need to apply sunscreen at least 20 minutes before you see sunshine, and according to New Zealand-based dermatologist Dr Christopher McEwan, 'Thick or very greasy sunscreens may need to be applied up to 45 minutes earlier as their constituency prevents them getting under the skin any faster.'

2. And make sure you put on enough of the stuff. The most common advice from suncare experts is that factor 15 is safe. 'However most people applying factor-15 sunscreen get protection of about an eight because they don't apply it properly,' says researcher Professor Brian Diffey. In a lab, sunscreen is tested in a layer so thick the average person would go through a bottle of sunscreen every four days. As most of us don't do this, experts now say that it's safer to apply a shot glass sized amount of factor 30+ to your whole body (including parts you don't think you expose to the sun such as the soles of your feet, one of the most common sites for melanoma).

3. Reapply sunscreen every 90 minutes. 'High factor sunscreens are a deception,' says plastic surgeon Dr Des Fernandes, founder of the Environ skincare range. 'Creams with a massive SPF factor only work at that level for a certain time.' Truth is that sunscreen gets weaker and weaker on exposure to the sun, and over time this cuts the percentage of rays it can screen out. The average sunscreen lasts 90 minutes before its protection has degraded enough to be a danger to the skin.

4. Appreciate that all sunscreens are not equal in the ingredients they contain - a good sunscreen protects against UVA and UVB rays, yet some screens don't offer UVA protection. Check your product is marked with an SPF and a four-star rating. New German research says savvy sun worshippers will look for creams which contain marine extracts. Photosomes which protect marine plants from drying out in the sun, can actually reverse some of the DNA damage that occurs when UV rays hit the skin - and this it what triggers skin cancer. Expect many ranges to launch with these next year, but in the meantime, try Phytomer's marine based sunscreens. Or, if you're off to the US, pick up some Bio-Astin, a new marine algae pill that has been shown in trials to reduce the risk of sunburn by 50 per cent and has been approved by the FDA for use alongside sunscreen for skin protection.

5. An estimated 30,000 people were affected by 'travellers' thrombosis' in the UK last year - it's a small number compared to the 25m who fly. Despite the headlines, only 6.6 per cent of clots are fatal and most can be treated. Those most at risk are those with a past history, who've had recent surgery or are less than a month post pregnancy. Women on artificial hormones and those who are very overweight are also at higher risk. The next five tips should help keep you safe:

6. Research by Dr John Scurr from the Middlesex Hospital studied 230 travellers over 50 on an eight-hour flight. He put half in surgical stockings (which help regulate blood flow) and half were left without - of these, 10 per cent developed small blood clots by the end of the flight. 'This showed a link between long-haul flying and the development of small thromboses,' he explains. 'Most of these resolve themselves but some could progress to larger clots and require treatment.' Doctors can prescribe surgical stockings for those they feel at risk from DVT, or try Scholl's Flight Socks, £1.95 from Boots.

7. You've probably also heard that you should pop half an aspirin before flights to help protect against DVT - it could help but it does come with a potential risk of stomach irritation and bleeding. However, a team at the University of Arizona Medical School compared the effects of aspirin with a natural product called pycnogenol which had previously been shown to strengthen blood capillaries. They found a small dose of pyconogenol, had the same effect as a dose of aspirin five times higher - and was without side effects. Try Holland & Barrett pycnogenol, £9.49 for 30 (although if you have any circulatory or heart disorders see your doctor first).

8. The main cause of DVT is slowed circulation which causes blood to clot. Once on the plane, you can help keep circulation moving by walking up and down or by rotating your ankles and clenching your calf muscles every 30 minutes.

9. Go to the gym before you get on the plane. 'Exercise has been shown to keep circulation pumping for four or five hours post workout,' says Mr Farrol Kahn director of the Aviation Health Institute.

10. While DVT can occur in anyone who sits still for a long time, it's believed air travellers are particularly prone because lowered oxygen levels in the cabin thicken the blood. Researchers from the Saitama Medical School in Japan found that eating a snack or drinking (non-alcoholic drinks that is) actually increased oxygen levels in the body by 21 per cent - and boosted brain levels by 48 per cent.

11. Jetlag is not just psychological. Research suggests that frequently crossing time zones shrinks your brain. There are theories on how to beat it, but latest studies say the stomach could be the key to the whole conundrum. Research from the University of Virginia shows that eating meals at appropriate times to the destination to which you are travelling for two days before the flight helps the body adjust more quickly to time changes - but the team don't know exactly why. 'We just know that the liver is normally the slowest organ of the body to adapt to changes in time zones,' says Naomi Ihara, lab manager and assistant to lead researcher Dr Michael Menaker. 'Normally it takes up to two weeks to adjust to a six-hour time zone shift - but when you alter food timings it takes just two days.'

12. Try alternative treatment for jetlag. Homeopaths recommend arnica and Cocculus Indicus, taken every 12 hours for two days before and three days after flying. 'The arnica works to get over the trauma,' says Tony Pinkus of homeopathic pharmacy Ainsworths. 'And the Cocculus helps balance the circadian rhythms'.

13. Avoid bugs when flying. Studies show the average airplane has thousands of bugs in the air at any time and this is one reason why so many of us get a cold a couple of days after a flight. To prevent this, rub a little oil into your nostrils when you board. 'Many diseases get into the immune system through tiny cracks in the nose which get enlarged in the dry cabin environment,' says Diana Fairchild, author of Jet Smarter (£9.99, Flyana Rhyma). 'Oiling inside the nostrils with a little olive, almond or jojoba can help prevent this.'

14. Pack some tea tree oil for the flight. Dr Farol Kahn says that sniffing a drop or two whenever anyone around you sneezes can help disinfect the nasal area before any germs take hold.

15. Worried about air turbulence? Get some ice from the cabin crew and pop it on your face. That's the advice from Dr Max E Levine, from Penn State University in Pennsylvania who found this helps stop travel sickness in its tracks. 'The cooling acts on the nervous system response that triggers nausea,' he explains. You'll also lower your risk of travel sickness by choosing the chicken or the pasta for your inflight meal - Levine's research showed that protein kept the stomach calmer than a carbohydrate meal or no food at all.

16. Beat hayfever. This is a matter of strengthening the immune system and reducing the amount of histamine the body triggers. 'Taking doses of quercetin (a bioflavonoid) can help do this by making the system less sensitive,' says leading natural therapist Dr John Briffa. 'This acts directly on the mast cells which release histamine and prevent them overreacting.' Best results come by combining 1,200mg quercetin with 1g vitamin C.

17. Watch what you eat. Dairy products can stimulate mucus production that makes the nasal passages more sensitive to generally innocuous invaders like pollen. Also watch your fruit intake. 'Many people who are allergic to tree pollen also react to many tree fruits,' says Dr Bill Franklin, consultant allergenist at the London Allergy Clinic (and the man who invented the pollen count). Most common culprits are apples, melons and stoned fruits such as plums and peaches.

18. Take a B-complex supplement, if you're prone to insect bites. Anecdotal evidence says high levels of vitamin B1 in the blood stop the bites. Take it before you travel - once one bite shows up more will follow. Remember that it takes 16 hours for the average bite to emerge on a 40-year-old, compared to 20 minutes on a six-year-old. Sunset is the worst time for bites so always apply insect repellent then.

19. Be careful what you eat. To beat stomach upsets, the most important thing you can do is avoid shellfish, poorly cooked meat, warmed-up rice, ice cubes and salads washed in unclean water. Avoid them all. Strengthening your stomach before your trip with supplements that increase levels of the bacteria that helps fight food poisoning may also help. Try supplements of acidophilus, or probiotics such as Seven Seas Multibionta, £4.45.

20. Don't always blame the prawns for that stomach upset. A major US report found that some outbreaks of Delhi Belly were actually linked to swallowed pool water. The culprit is a germ called cryptosporidium which gets into pool water when an infected person (most commonly a baby or toddler) has what those in the trade call a faecal accident. 'One recent study monitoring these showed one pool in England estimated someone has this type of "accident" three times a week,' says Dr Rachel Chalmers from the Public Health Laboratory Service. 'If that person were infected and you swallowed water, it could lead to infection.' On that note, we'll leave you, but just to say cryptosporidium can also be passed on through direct person-to-person contact and by touching infected animals - wash your hands before eating and we'll all have a safer, happier summer.