The Ordinary Glycolic Acid 7% Toning Solution

Glycolic Acid is an alpha hydroxy acid that exfoliates the skin. 
This
7% toning solution offers mild exfoliation for improved skin radiance
and visible clahis pH of this formula is approximately 3.6. Glycolic
Acid has a pKa of 3.6 and pKa is the most important aspect to consider
in formulating with acids. pKa implies acid availability. When pKa is
close to pH, there is an ideal balance between salt and acidity,
maximizing effectiveness of the acid and reducing irritation. Higher pH
numbers in such a case would increase salt which counter-intuitively
would make the formula even more irritating than if the formula was more
acidic.

Note:
While exfoliating acids can result in quick visible benefits, we
generally suggest indirect forms of skin exfoliation in favour of direct
forms such as this formula due to potential inflammation and
sensitivity associated with acids. The formula also improves the
appearance of skin texture with continued use.
Use
ideally in the PM, no more frequently than once per day. After
cleaning, saturate a cotton pad with the formula and sweep across face
and neck. Avoid the eye contour and contact with eyes. Do not rinse off.
Continue with additional skin treatments as needed. Contact of the
product with the skin must be of limited frequency or duration. If
irritation occurs, cease use and consult a physician. Use only as
directed on unbroken skin. Patch testing prior to use is advised.

Sunburn
Alert: This product contains an alpha hydroxy acid (AHA) that may
increase your skin's sensitivity to the sun and particularly the
possibility of sunburn. Use a sunscreen, wear protective clothing, and
limit sun exposure while using this product and for a week afterwards.