- What are the benefits of
using lactic acid and lactates over other organic acids and what are the
recommended usage levels?
- What is the difference
between L(+), D(-) and DL (racemic) lactic acid?
- How is lactic acid produced
and is it related to milk?
- What is the stability of
L(+)-lactic acid and lactates?
- How can I regulate the pH?
- In which phase of the
production should I add lactic acid/lactates?
- Which thickeners can be
used to obtain a stable formulation?
- How can I produce a mild
formulation (sensitive skin/no risk of irritation) with lactic
acid/lactates?
- Are the lightening
properties of lactic acid/lactates based on peeling/exfoliating
properties?
- Is it possible to safely
use higher concentrations of lactates?
- Which claims can be made
when incorporating lactic acid/lactates in formulation?
1. What are the benefits of using lactic acid and lactates over
other organic acids and what are the recommended usage levels?
PURAC L(+)-lactic acid and lactates offer
the formulator a unique combination of properties. The presence of lactic acid
or lactates depends on the pH. In most cosmetic products the pH is around 5.5,
and at this level hardly any lactic acid is present. The benefits and usage
levels of lactates depend on the desired functionality:
|
Desired functionality
|
Mainproduct
|
Recommended usage level [%]
|
Remark
|
|
pH-regulation
|
PURAC 90%
|
< 0.5
|
|
|
Moisturizing
|
PURASAL 60%
|
0.5 - 5
|
|
|
AHA effect*
|
PURAC 90%
|
3 - 5
|
pH 4.0 - 5.0
|
|
Skin lightening
|
PURASAL 60%
|
13 - 15
|
pH 5.5 - 7.0
|
CTFA recommends the addition of an SPF for
AHA formulations
Additional properties of lactates are antimicrobial efficacy, humectancy and
improved skin feel. No other organic acid combines such a variety of
properties. PURAC L(+)-lactic acid: one compound, many benefits.
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2. What is the difference
between L(+), D(-) and DL (racemic) lactic acid?
Lactic acid is the simplest hydroxy acid
with a chiral carbon atom. Due to this chirality lactic acid exists in a
racemic form and in two optically active forms: L(+) and D(-). Only the L(+)
form is the natural form and is present in the human body (e.g. skin, muscles
and brain). Tests show that only the L(+) form is recognized by the skin, and
that it also exhibits the least irritation. The D(-) form lacks some of the
benefits of the L(+) form and the racemic mixture only partly possesses the
benefits of the L(+) form. PURAC's L(+) form is also available in USP and EP
grades. L(+)-lactic acid: the natural isomer of lactic acid.
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3. How is lactic acid produced and is it related to milk?
PURAC L(+)-lactic acid and lactates are
100% natural products, with carbohydrates (such as beet sugar) as their raw
material. The production process (fermentation with the aid of bacteria) is
also natural. In addition to L(+)-natural lactic acid, there is also so-called
synthetic lactic acid available on the market. This product is less suitable
for use in cosmetic formulations because it triggers irritation and is only 50%
active. If lactic acid or lactates are to be used in cosmetic products, always
insist on natural L(+)-lactic acid!
Because lactic acid (officially known as 2-hydroxy propionic acid) was first
discovered in 1780 by the Swedish chemist Scheele in a sample of spoiled milk,
it was named lactic acid. There is no other relation to milk and PURAC
L(+)-lactic acid and lactates (sodium and potassium lactate) are clear, water
white and low-viscous liquids with a mild odor. All other mineral salts are
powders.
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4. What is the stability of L(+)-lactic acid and lactates?
L(+)-lactic acid and lactate salts are
very stable, resulting in a shelf life of 5 years. L(+)-lactic acid is a
self-preserving acid so the product does not come under attack by micro-organisms.
In most commonly used temperature areas (0°C/32°F to 200°C/392°F), L(+)-lactic
acid and lactate salts are completely stable.
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5. How can I regulate the pH?
PURAC (in combination with PURASAL) can be
used to regulate the pH in all kinds of toiletry and skin care products. In
liquid products, the addition of 0.1-0.5% wt of PURAC is, in most cases,
sufficient to produce a pH of 5-6 in the end product.
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6. In which phase of the production should I add lactic
acid/lactates?
Lactic acid and lactates can best be added
in the aqueous phase.
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7. Which thickeners can be used to obtain a stable formulation?
Stabilizing
products containing hydroxy acids and their salts can be a problem, since
typical usage levels can be relatively high. This can result in a formulation
that is very acidic and/or has high levels of salt (ions). Thickening systems
such as Carbopol thickeners are therefore not compatible. Most thickeners
however are compatible. These include xanthan gum, methyl cellulose and hydroxy
ethyl cellulose.
Thickeners
compatible with PURAC (lactic acid) are:
|
Chemical name
|
Product
|
Supplier
|
Stable at
50°C / 122°F
|
|
Methyl cellulose
Xanthan gum
Hydroxy ethyl cellulose (HEC)
Methyl hydroxy ethyl cellulose
Poly vinyl pyrrolidone (PVP)
Synthetic copolymer
Acrylic copolymer
|
Methocel 311
Kelzan ASX
Natrosol 250HR
Culminal MHEC
Luviskol K90
Solagum SH210
Alcogum L
|
Dow
Kelco
Hercules
Hercules
BASF
Seppic
Alco
|
No
Yes
Yes
Yes
Yes
Yes
Yes
|
The following thickeners are compatible with PURASAL (sodium or potassium
salt):
|
Chemical name
|
Product
|
Supplier
|
Stable at
50°C / 122°F
|
|
Methyl cellulose
Hydroxy ethyl cellulose
Hydroxy propyl cellulose
Poly vinyl pyrrolidone
Synthetic copolymer Carboxy Methyl Cellulose (CMC)
|
Methocel 311
Natrosol 250HR
Klucel 99H
Luviskol K90
Solagum SH210
Cekol
|
Dow
Hercules
Hercules
BASF
Seppic
Noviant
|
No
Yes
No
Yes
Yes
Yes
|
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8. How can I produce a mild formulation (sensitive skin/no risk
of irritation) with lactic acid/lactates?
Lactic acid and lactates are very effective in producing mild formulations. Commercial
products for sensitive skin and/or baby products often contain PURAC lactic
acid and lactates. In order to obtain such a mild formulation it is important
to set the pH of the formulation at 5.5 - 7.0. If formulated at these pH
levels, mild and gentle cosmetic products can be obtained that are suitable for
all skin types.
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9. Are the lightening properties of lactic acid/lactates based
on peeling/exfoliating properties?
No, the lightening properties of lactic acid/lactates are based on the
suppression of the formation of tyrosinase. As a result, the lightening effect
can be achieved at (skin) neutral pH conditions (pH 5.5-7.0). Only a few active
ingredients are currently known to have tyrosinase-formation suppression
abilities. The best known active is L(+)-lactic acid and its salts. Good
skin-lightening properties have been reported at higher concentrations (>5%
equivalent lactic acid), making use of the independent melanogenic controlling
function of the viable pigment cell. If formulated at lower pH levels, it is
presumed that the exfoliative action of L(+)-lactic acid and lactates in some
way could contribute to the lightening effects of the compositions tested.
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10. Is it possible to safely use higher concentrations of
lactates?
Yes, it is quite possible to formulate with high concentrations of lactic acid
or sodium lactate. Concentrations up to 15% have been reported in commercial
products. The most important parameter to watch is the pH of the final
formulation. As long as the pH of the formulation is higher than 5.0, mild and
gentle products can be formulated with higher concentrations of lactic acid (up
to 10% PURAC 90%) and/or lactates (up to 15% PURASAL S 60%). The final CIR
report from June 1997 states that lactic acid is safe in concentrations =10% at
a final formulation pH of = 3.5.
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11. Which claims can be made when incorporating lactic
acid/lactates in formulation?
The possible claims are:
·
Contains
natural moisturizer
·
With NMF
·
Contains AHA
·
Contains fruit
acid
·
With natural
skin-lightening ingredient
·
Exfoliating action
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