We're sorry to use the A-word, but that chill down your neck and the should-I-shouldn't-I decisions around central heating spell only one thing: Autumn is on its way.
As well as digging out your woollies, the other think that marks the change in seasons are the hordes of people sniffling and sneezing in your train carriage, on the street and in your office.
Dr Paul Zollinger-Read, chief medical officer for Bupa and HuffPost UK blogger says: "“The common cold is a mild infection that causes a blocked or runny nose, sore throat, sneezing and a cough. It’s caused by several viruses from lots of different families but the most common cause is the rhinovirus. Half of colds are caused by this but in the autumn it can cause up to 80% of colds.
“Seasonal flu is caused by two types of virus: influenza A and B (C is a very rare type). The symptoms are the same as colds but more severe. You may also get a fever, shivering, a headache, a dry cough and aching muscles."
Dr Nitin Shori, medical director of the Pharmacy2U Online Doctor service, NHS GP and HuffPost UK blogger agrees, adding that colds and flu are certainly much more prevalent in the winter months.
“Colds are often accompanied by a runny nose, sneezing, cough, headache, sore throat and mild fever, which usually develop over the course of a few days," he says. "Flu can have similar symptoms, although the illness tends to come on more quickly and severely, with sudden fever, plus aching muscles and the feeling of exhaustion."
We all have theories about what makes us catch a cold or develop flu, but what is the official version?
Dr Zollinger-Read says: "“Colds and flu spread the same way – through direct contact or through the air when someone coughs or sneezes. They can also be picked up when you touch a contaminated surface and then put your fingers near your nose, mouth or eyes.
"The flu virus can live on hard surfaces for up to 24 hours and a on a soft surface for around 20- minutes. Practising good hygiene is essential to helping prevent and to stop colds and flu from spreading. Wash your hands regularly – making sure you use hot, soapy water.
"Don’t share towels with anyone and keep hard and soft surfaces, like door handles, toys and bedding, clean. You can also help stop them spreading by covering your nose and mouth when you cough or sneeze and throwing away used tissues as soon as you’ve used them."
Stress can also play havoc with your immune system, but do everything you can to boost it. If you feel a cold coming on, paracetamol and Zinc supplements have been touted as they best form of prevention, but Evelyn Toner, consultant dietician at London Bridge Hospital says it's good to be mindful of your stress levels.
"The National Institute of Mental Health explains how different people will feel differently in response to stress, for instance some may experience digestive symptoms, while others may have headaches, sleeplessness, depressed mood, anger and irritability.
"People under chronic stress are prone to more frequent and severe viral infections, such as the flu or common cold, and vaccines, such as the flu shot, are less effective for them (NIMH). Over time, there may be an increased risk of serious health problems such as heart disease, high blood pressure, diabetes, depression, anxiety disorder, and other illnesses (NIMH)."
Finally, if you do fall ill, should you call your doctor?
Dr Shori advises: “People often wonder whether they should contact a doctor when they have a cold or flu.
The truth is that viruses can’t be treated by antibiotics and more often than not, resting, staying hydrated and taking non-prescription remedies to ease the pain and reduce the fever, is all that’s needed. However, you should consult a medical professional if you’re worried your condition is developing into something else, your symptoms are worsening, or you’re in a high risk group."
“Preventative measures are important. A healthy lifestyle can give your immune system a boost and leave you less susceptible to illness. Colds and flu are both passed on from person to person, usually through coughing and sneezing, so hygiene is important too.
Top tips for de-stressing and boosting your immune system:
Dr Tom Stevens, consultant psychiatrist at London Bridge Hospital says:
"Realistic balance in all aspects of your life is probably the most important step to manage stress - particularly the balance between work, life and family.
1. Make time for music, art, reading, cinema, sport, dance, or anything else that interests you.
2. Spend time with people you care about including family and friends. Think about who you do spend time with and ask yourself the question "do I want to spend time with them?"
3. Take regular exercise.
4. Learn the art of relaxation. This is not watching thrillers on television or drinking with friends, but something like yoga, hot baths, meditation or lying on a beach which allows your mind to rest.
5. Live in the past, present and future. Don't fall into the trap of constantly ruminating about the future and forgetting to enjoy the present. If this is difficult, look at a raisin for 15 minutes and think about what might be interesting about it!
6. Be careful not to use alcohol, drugs, food, sex or gambling to manage the mood swings.
7. Learn to say "no" and delegate.
8. Think about what is important for you - "there is more to life than going faster"
9. Are you avoiding anything? Deal with bills, difficult conversations and problems with colleagues or family.
10. Do you do anything that is not motivated by power, money and sex? If the answer to this is no then return to number 1 and think of something."