Every Monday, we’ll answer your questions on Covid-19 and health in a feature published online. You can submit a question here.

This week, HuffPost UK reader Helen asked: “What is the damage to your health by wearing masks?

There’s very little evidence that wearing face masks – we’re talking the blue surgical ones and cloth coverings that most of the public are wearing – is harmful to your health.

“This is one of those areas where conspiracy theories and science conflict,” Paul Hunter, a professor in medicine at the University of East Anglia, tells HuffPost UK.

Some social media posts suggest mask-wearing could lead to hypoxia, a dangerous condition when your body doesn’t get enough oxygen. There are even extreme claims floating about that mask-wearing could lead to death.

One cause for confusion is the difference between surgical masks and cloth coverings, and the N95 respirators that are designed for use in healthcare settings – we need to differentiate between them as their health impacts vary.

With ordinary face coverings and surgical masks, there is very little to worry about in terms of risk to health.

“Probably the most common issue is irritation and occasionally dermatitis,” says Prof Hunter.  “I do not think there is any real evidence for these face coverings and masks interfering with adequate breathing.”

How to use face masks safely

Prof Hunter stresses that ordinary face masks do need to be changed regularly (every five hours, he suggests) especially if wet or dirty – and they need to be disposed of safely, or washed each day in the case of coverings, after use. 

The World Health Organisation (WHO) advice is to “make wearing a mask a normal part of being around other people”, as part of a comprehensive strategy to “suppress transmission and save lives”.

However, it does recognise that wearing any types of face mask can lull people into a false sense of security and make us less likely to social distance or practice other safety measures, such as washing hands, that are just as critical to curbing the spread of Covid-19. 

We must also be aware of the risks of self-contamination, for example if you keep touching your face to pull your mask down, and inadvertently transfer virus to the inside of your mask. Try not to keep touching your mask, and if you do, take hand sanitiser with you so you’re keeping your hands clean. 

What’s the deal with N95 masks?

The evidence of risk with N95 masks is “stronger”, Prof Hunter explains.

Studies have demonstrated certain side effects associated with the use of these respirators. We do know, for example, that wearing these fitted masks for long periods without a break could potentially affect your oxygen levels – but  probably not to a harmful extent.

Some of the side effects linked to wearing N95 masks include: facial dermatitis, increased work of breathing, respiratory fatigue, impaired work capacity, increased oxygen debt, early exhaustion at lighter workloads, elevated levels of CO2, increased nasal resistance, and increased noncompliance events leading to self-contamination (for example, by touching your face), says Prof Hunter.

“I personally would not encourage the general public to wear N95 respirators as a protection against Covid,” he adds. That said, many healthcare professionals show no side effects, despite wearing these N95 masks day in day out.

One study even found exercising with N95 masks to be safe. Researchers concluded that in healthy subjects, short-term moderate-strenuous aerobic physical activity with a mask is “feasible, safe, and associated with only minor changes in physiological parameters, particularly a mild increase in EtCO2”.

However, they did caution that subjects suffering from lung diseases should be wary before attempting physical activity with any mask. And this is reaffirmed by another study, which showed people with chronic obstructive pulmonary disease (COPD) struggled with breathlessness after wearing N95 masks.

Who is exempt from wearing a mask?

• Children under the age of 11 (or under the age of five in Scotland)

• People who have a physical or mental illness or impairment, or a disability that means they cannot put on, wear or remove a face covering.

• People for whom putting on, wearing or removing a face covering would cause severe distress.

• People travelling with, or providing assistance to, someone who relies on lip reading to communicate.

• People travelling to avoid injury or escape the risk of harm.

Experts are still learning about Covid-19. The information in this story is what was known or available at the time of publication, but guidance could change as scientists discover more about the virus. To keep up to date with health advice and cases in your area, visit gov.uk/coronavirus and nhs.uk.