Under a dryer, the dryer is heating up the water that is on your hair, in your hair and on your scalp and recirculating whatever whatever water is underneath the cap. With the addition of heat, the hair should absorb some of that water and the conditioner.
The steamer is heating up water and forcing it out, due to the increased temperature the strands should absorb this water. In this situation the hair is subjected to more water than with the dryer with the possibility of absorbing more water because it is receiving more water.
I think under certain conditions the dryer could be more drying to the hair and scalp than the steamer. And for some the steamer may cause their hair to become over moisturized because of the high amounts of water the hair can absorb.
Short Answer: The steamer will bombard the hair with far more water than is possible with a dryer and plastic cap.
Under a dryer, the dryer is heating up the water that is on your hair, in your hair and on your scalp and recirculating whatever whatever water is underneath the cap. With the addition of heat, the hair should absorb some of that water and the conditioner.
The steamer is heating up water and forcing it out, due to the increased temperature the strands should absorb this water. In this situation the hair is subjected to more water than with the dryer with the possibility of absorbing more water because it is receiving more water.
I think under certain conditions the dryer could be more drying to the hair and scalp than the steamer. And for some the steamer may cause their hair to become over moisturized because of the high amounts of water the hair can absorb.
Short Answer: The steamer will bombard the hair with far more water than is possible with a dryer and plastic cap.