Cold winter air tends to be dry, and indoor heating systems further contribute to the lack of humidity. This dryness can lead to moisture loss from your hair, making it more prone to dryness, frizz, and breakage.
The scalp produces less sebum (natural oils) in colder weather. Sebum helps in maintaining the moisture balance of the hair. When its production decreases, the hair is more susceptible to dryness and brittleness.