Inclusion Criteria:

• * Participants must qualify for one of the following scalp conditions based on clinical opinion of a board-certified dermatologist: healthy scalp, dandruff, seborrheic dermatitis, or hair loss disease
• * All Women of Child Bearing Potential must indicate use of two of the following contraceptive methods. The WaterPik device uses an ultrasonic technology which includes ultrasound. Unnecessary ultrasound is not recommended for pregnant women.
• * Combined (estrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation (oral, intravaginal, or transdermal)
• * Progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable, or implantable)
• * Intrauterine device (IUD)
• * Intraurerine hormone-releasing system (IUS)
• * Vasectomized partner
• * Sexual abstinence
• * Barrier method, such as a condom

Exclusion Criteria:

• * Non-English speaking
• * Exclusion related to pregnancy, lactation, or plans to become pregnant over the course of the study (based on self-report from the participant)
• * Current clinical condition that, in the opinion of the site investigator, would interfere with adherence to study requirements