Frizzy hair is typically caused by a lack of moisture in the hair shaft, which makes the hair more prone to absorbing humidity from the air. This absorption causes the hair cuticles to swell and rise, leading to a rough, textured, and often uncontrollable appearance. Several factors can contribute to frizzy hair, including:

1. Humidity: High levels of humidity in the environment can cause the hair to absorb moisture, leading to frizz.
2. Lack of Moisture: Dry hair is more susceptible to frizz as it seeks moisture from the surrounding air.
3. Damaged Hair Cuticles: Chemical treatments (like coloring or straightening), excessive heat styling, and mechanical damage (from brushing or combing too harshly) can damage the outer layer (cuticle) of the hair, making it easier for moisture to penetrate and cause frizz.
4. Porosity: If your hair has high porosity, meaning it easily absorbs and loses moisture, it is more likely to become frizzy.
5. Hair Type: Naturally curly or wavy hair tends to be more prone to frizz due to its structure, with the curls creating spaces for humidity to enter.
6. Product Buildup: The use of heavy products or not rinsing hair thoroughly can lead to residue buildup, which can interfere with the hair's ability to retain moisture and contribute to frizz.
7. Health and Diet: A poor diet lacking in essential vitamins and minerals can affect hair health, making it more prone to dryness and frizz.

To manage frizzy hair, it's important to maintain proper hair hydration, use moisturizing and smoothing hair products, protect hair from heat and chemical damage, and consider using anti-frizz serums or oils. Additionally, gentle washing and conditioning routines, along with regular deep conditioning treatments, can help to seal the hair cuticles and reduce frizz.