Tea Tree (Melaleuca alternifolia) has excellent antifungal and antiseptic properties and here is some Research done on Tea Tree exploring this.  If you would like to read the article on antifungal properties you can find it here.

Study 1 

Journal of the American Academy of Dermatology
December 2002, Volume 47, Issue 5, Pages 852 – 955
DOI: https://doi.org/10.1067/mjd.2002.122734

Treatment of dandruff with 5% tea tree oil shampoo

Andrew C. Satchell, MB, BS, Anne Saurajen, MB, BS, Craig Bell, BSc(Hons), PhD, Ross StC. Barnetson, MD

Abstract

Background:

Dandruff appears to be related to the yeast Pityrosporum ovale. Tea tree oil has antifungal properties with activity against P ovale and may be useful in the treatment of dandruff.

Objective:

We conducted a randomized, single-blind, parallel-group study to investigate the efficacy and tolerability of 5% tea tree oil and placebo in patients with mild to moderate dandruff.

Methods:

One hundred twenty-six male and female patients, aged 14 years and older, were randomly assigned to receive either 5% tea tree oil shampoo or placebo, which was used daily for 4 weeks. The dandruff was scored on a quadrant-area-severity scale and by patient self-assessment scores of scaliness, itchiness, and greasiness.

Results:

The 5% tea tree oil shampoo group showed a 41% improvement in the quadrant-area-severity score compared with 11% in the placebo group (P < .001). Statistically significant improvements were also observed in the total area of involvement score, the total severity score, and the itchiness and greasiness components of the patients’ self-assessments. The scaliness component of patient self-assessment improved but was not statistically significant. There were no adverse effects.

Conclusion:

Five percent tea tree oil appears to effective and well tolerated in the treatment of dandruff.

Study 2 

American Journal of Orthodontics and Dentofacial Orthopedics
Volume 145, Issue 2, February 2014, Pages 198-202
https://doi.org/10.1016/j.ajodo.2013.10.015

Antimicrobial effect of Melaleuca alternifolia dental gel in orthodontic patients

Milton SantamariaJr, Klodyne Dayana Petermann, Silvia Amélia Scudeler Vedovello, Viviane Degan, Adriana Lucato, Cristina Maria Franzini

The aim of this study was to evaluate the antimicrobial effect and sensorial analysis of the gel developed with the essential oil of Melaleuca alternifolia.

Thirty-four volunteers, divided into 2 groups, were monitored for 4 weeks.

Initially, clinical biofilm (plaque index) and saliva samples (bacteria count) were collected, from which the standard values for each patient were obtained.

For 7 days, group 1 used the melaleuca gel (Petite Marie/All Chemistry, São Paulo, Brazil), and group 2 used Colgate Total (S.B. Campo, São Paulo, Brazil). After 7 days, the plaque index was performed again, as well as the bacteria count and the sensorial analysis (appearance, color, odor, brightness, viscosity, and first taste sensation).

The volunteers were instructed to return to their usual dental hygiene habits for 15 days.

After this, group 1 started using Colgate Total, and group 2 started using the melaleuca gel, with the same evaluation procedures as the first week.

The data were analyzed statistically with a significance level of 5%.

In the bacteria count and clinical disclosure, the melaleuca gel was more effective in decreasing the dental biofilm and the numbers of bacteria colonies. According to the data from the sensory evaluation, Colgate Total (the control) showed better results regarding flavor and first sensation (P <0.05).

We concluded that melaleuca gel is efficient in bacteria control but needs improvement in taste and first sensation.