The soothing effect of fresh air is phenomenal. Many times babies who are other wise well but keep crying inspite of being fed and even after giving colic aid, suspecting colic pain, stop crying the moment they are taken to the fresh air! Such is the power of fresh air, it soothes the nerves. What applies to babies applies to adults too, who are many times found to  be silently suffering from lack of fresh air. This may result in reduced performance levels and even our sleep may not be very sound and we may not be feeling rested and refreshed in the morning.
Lack of it
Lack of fresh air affects us in many ways, apart from  reducing oxygen intake, there are many irritating gases and smells that are being continuously generated inside the house that is not liked by the human body. When the weather is hot, these are felt more. In warm weather or when we are physically active inside the house, the need for fresh air is greater. We need to make, provision for fresh air to enter the house as much as possible.
South-west monsoon is the summer monsoon
Even as it pours heavily with lots of thunder and lightning, the weather may become a little cold, but soon after, the sun shines sharply and we maybe feeling the heat more than we used to in the beginning of summer. Even a cup of hot tea with breakfast or hot meals, brings a bout of sweating and we may start wondering about the state of our health. This is because rain adds to the water content in the atmosphere and evaporative cooling is not very effective as it is more humid after the rains. We may be sweating but it does not evaporate easily.
The sun’s role
We don't have to blame the hot sun for the heat because it is this very hot sun that evaporates sea water and brings it over land. The sun during summer monsoon is hot as the northern hemisphere where we are located in India is turned towards the sun and in fact it will take a few more months for it to turn away. Therefore as long as the hot weather season lasts, which incidentally is not just the three months of actual summer but includes the summer monsoon rainy season as well which adds to another three months of warm weather.
Keep windows open
This is the reason why we need to keep the windows open even as the rainy season has started. The temperature may be lower but with added humidity, we need good breeze to keep us feeling comfortable. We need to have proper rain control devices like horizontal projections,  sun shades  which while avoiding rain entry allows breeze to enter the house. During the hours of actual rain, if it becomes cold, then some of the window shutters on the windward side can be kept closed.
Many times it is assumed that once the rainy season has started, we don’t have to keep the windows open. But without natural ventilation in this season, the discomfort level may be much higher than it was during the beginning of summer.
Even our bathrooms need good ventilation during this season. Infact if you try to have a long and hot shower bath like you do during the winter months, you are sure to feel the high humidity very uncomfortable and you will wish for a breath of fresh air.
Problems of humidity
Higher humidity with higher temperature brings in its wake its own problems.
Though we all appreciate the fresh smell of soil after the first rains, things rot fast in this weather and smell of sweating and body odours are felt more. You may feel like changing your clothing twice a day. Though in a city like Bangalore, which is some three thousand feet above sea level, the humidity is usually less and the weather is much cooler. Near sea level, the combination of heat and humidity can make the inside of the house more uncomfortable than the outside under shade. This is the reason why we should have greater access to fresh air inside our houses.