I booked a taxi the other day. When I boarded, I noticed an exhaust-like smell in the cabin. All the windows were closed and the air-conditioning was set to "recirculation". Where is this smell coming from and how dangerous is this? The driver seemed okay, but I felt a little nauseous at the end of the trip.

In some cars, it is possible for some outside air to enter the cabin - even with the air-conditioning in recirculation mode. So, when the vehicle passes a foul-smelling area - whether it is a polluted canal, a smoke-belching vehicle or an industrial area - you may still get a whiff.

In such a situation, do not lower the windows immediately as this will only aggravate it. Instead, wait till you are some distance away to wind down the windows.

But if you constantly smell exhaust fumes in the car, there may be a leak in the door, window or boot weather seal. With the exhaust outlet at the rear of the car, the first place to check is the boot or tailgate rubber seal.

Often, the turbulence at the rear of the car will lead to exhaust gases streaming into the boot space if the seal around the boot or tailgate lid or tail lamp is broken.

In many cars, there is no spatial isolation between the luggage compartment and passenger cell. So, exhaust gases that enter the boot are also likely to get into the cabin.

This is a dangerous situation and should be rectified urgently. Prolonged inhalation of any exhaust fumes is harmful to the respiratory system.