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Table 1 Criteria for selection of big toenail and hair samples

From: Big toenail and hair samples as biomarkers for fluoride exposure – a pilot study

Criteria for selection of big toenail samples

 • No dermatological disease, trauma or injury affecting the nails.

 • No nail polish or any other chemicals on nails for at least three months before the date of nail sample collection.

 • The patients were notified about the study in advance and advised not to cut their nails for four weeks before sample collection. Patients who had nail polish or any other chemicals on their nails waited for three months and then one extra month for nails to grow before sample collection, i.e. four months.

Criteria for selection of hair samples

 • No dermatological disease affecting the hair.

 • No dyed or bleached hair. Hair was free of creams, oil and gels before sample collection.

 • The patients were informed six weeks in advance about the study and instructed about the dates for hair sample collection and also advised that they should not get a hair-cut during this time. If a patient has had a hair-cut, perm or colouring during the last six weeks, sample collection was postponed for six weeks as hair grows at about 0.4 mm/day or an average of about 1 cm/month.