Live your best life & take care
Using the right amount of a skin care product is as important as picking the right product(s). If you don't apply enough of the product or for a too short duration, you will not get the optimal result. This is particularly crucial when using sunscreen to reach the sufficient SPF level and protection. According to a study published in the Journal of the American Academy of Dermatology by Andreas Storm MD et al. 95% of patients with a topical treatment under-dose, hence do not use enough cream.
If there is a specific user manual mentioning the dosage, or you got a prescription, follow their recommended instructions. If the product came without specific dosage instructions, there is a general rule of thumb. The recommended amount of product to apply varies, depending on the product type.
THE 2 FINGERS RULE FOR SUNSCREEN
For sunscreen you need 1/2 teaspoon for the face or enough to cover the bottom of a shot glass and a full shot glass for the body, which should add up to 2mg per cm2. Another method is using the "rule of nines, which is used for burns. The body areas are divided into 11 area's, each representing 9% of the total. Sunscreen can be applied to each of these areas at a dose of 2 mg/cm2 (regardless phototype) if two strips of sunscreen are squeezed out on to both the index and middle fingers from the palmar crease to the fingertips, thus 2 fingers. (1)
The body areas are:
1 Head, neck, and face
2 Left arm
3 Right arm
4 Upper back
5 Lower back
6 Upper front torso
7 Lower front torso
8 Left upper leg and thigh
9 Right upper leg and thigh
10 Left lower leg and foot
11 Right lower leg and foot
For the use of other topical products there is a guidance created called Finger Tip Units or FTU's by CC Long and AY Finlay. It is a way of measuring the amount of product squeezed out of a tube with a 5mm diameter nozzle and applied from the distal skin-crease (the crease closed to the fingertip) to the tip of the index finger.
The FTU concept has been used as a central part of an education programme for parents of children with atopic eczema, has been advocated to reduce the variation in usage of topical steroids and to encourage adherence to therapy. For a serum, you may need less as they are lightweight products which should be fully "absorbed" without residue. If the skin still feels sticky after 1 minute, you probably applied too much product. A guidance would be a pea size dot on forehead, right cheek, and left cheek, which is similar to the recommended amount of retinoids (Vitamin A). However, unlike Vitamin A, using too much serum usually isn't harmful for the skin, but increases the risk of "pilling".
The precise number of FTU's required:
One FTU covers 286 cm2, more specifically in males and 312 cm2 in females 257 cm2.
The quantity of cream in a fingertip unit varies:
Adult male: 1 fingertip unit provides 0.5 g
Adult female: 1 fingertip unit provides 0.4 g
Keep in mind this is a general guideline and the amount of product needed or results may vary also depending on skin type, concerns and the products particular attributes.
Take care (in the right amount and duration)
1. BMJ. 2002 Jun 22; 324(7352): 1526.Simple dosage guide for suncreams will help users Steve Taylor et al.
Illustration Tinea incognito with unjustified use of potent Topical Corticosteroids: a case series July 2017 International Journal of Basic & Clinical Pharmacology 6(8):2087 Haiya Sheth et al.
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