• Knowledge of nail unit anatomy and physiology and an understanding of nail plate growth and physical properties are
important prerequisites for understanding nail cosmetics.
• Disruption and excessive manipulation of certain nail structures, such as the hyponychium and eponychium/cuticle, should be
discouraged during nail cosmetic procedures and nail salon services.
• In addition to beautifying natural nails, nail cosmetics are beneﬁ cial in camouﬂ aging unsightly medical and infectious nail
problems, especially during the lengthy treatment period.
• Some nail cosmetics provide a protective coating for fragile, weak, and brittle nails.
• Proper nail grooming is crucial for maintaining nail health.
• Although most nail cosmetics are used safely, it is important to be aware of potential complications associated with nail
cosmetic materials and application processes.
Nail p hysiology and g rooming
Part 2: Nail Cosmetics
Introduction: Nail p hysiology
Nail u nit a natomy
Understanding nail unit anatomy is an essential ﬁ rst step to
comprehending the complexity of nail cosmetics use, includ-
ing pathology induced by cosmetic materials and proce-
dures. The nail unit is composed of the nail matrix, proximal
and lateral nail folds, the hyponychium, and the nail bed
(Figure 26.1 ).
Table 26.1 lists common nail signs and deﬁ nitions relevant
to nail cosmetics.
Nail m atrix
The nail matrix is comprised of germinative epithelium from
which the nail plate is derived (Figure 26.2 ). The majority
of the matrix underlies the proximal nail fold. The distal
portion of the nail matrix is the white lunula visible through
the proximal nail plate on some digits. It is hypothesized that
the white color of the lunula can be attributed to both
incomplete nail plate keratinization and loose connective
tissue in the underlying dermis. The proximal nail matrix
generates the dorsal (superﬁ cial) nail plate, while the distal
nail matrix generates the ventral (inferior) nail plate. This
concept is crucial to understanding nail pathology. Preserving
and protecting the matrix during nail cosmetic processes is
essential for proper nail plate formation. Signiﬁ cant damage
to the nail matrix can result in permanent nail plate
The nail plate is derived from the nail matrix and com-
posed of closely packed, keratinized epithelial cells called
onychocytes. Cells in the matrix become progressively ﬂ at-
tened and broadened and lose their nuclei as they mature
into the nail plate. The nail plate is curved in both the lon-
gitudinal and transverse planes, allowing for adhesion to the
nail bed and ensheathment by in the proximal and lateral
nail folds. Longitudinal ridging may be present on both the
dorsal and ventral surface of the nail plate. Mildly increased
longitudinal ridging on the dorsal nail plate is considered a
normal part of aging. Ridging on the ventral surface of the
nail plate is caused by the structure of the underlying nail
bed and vertically oriented blood vessels. The composition
and properties of the nail plate are further discussed below.
Nail f olds
The nail folds surround and protect the nail unit by sealing
out environmental irritants and microorganisms through
tight attachment of the cuticle to the nail plate. The cuticle
is often cut or pushed back during cosmetic nail procedures
which can allow moisture, irritants, bacteria, and yeasts
under the nail fold, resulting in infection or inﬂ ammation
of the nail fold, termed paronychia (Figure 26.3 ). Chronic
1 and Heh Shin R. Kwak
1 Oregon Dermatology and Research Center, Portland, OR, USA
2 Knott Street Dermatology, Portland, OR, USA
Cosmetic Dermatology: Products and Procedures Edited by Zoe Diana Draelos
© 2010 Blackwell Publishing Ltd. ISBN: 978-1-405-18635-3
ADORNMENT Nail Cosmetics
of nail plate
Distal groove Lateral nail fold
Figure 26.1 Nail unit with lines indicating important structures .
Nail matrix (nail root)
Cuticle (stratum corneum of the nail fold)
Figure 26.2 Diagram of the nail unit.
Figure 26.3 Paronychia.
Table 26.1 Common nail signs associated with or helped by nail cosmetics.
Nail sign Deﬁ nition Association
Onycholysis Separation of the nail plate from the nail bed Vigorous cleaning of hyponychium
exacerbates. Polish hides
Onychorrhexis Increased longitudinal ridging Associated with aging, distal notching.
Polish may help
Onychoschizia Lamellar splitting of the free end of the nail plate
Paronychia Inﬂ ammation of the nail fold
Dyschromia yellow Staining of the surface of the nail plate yellow
from the dye in nail polish
Green/black discoloration Pseudomonas is a bacteria that generates a
green – black pigment that discolors the nail plate
Nail bed changes as in psoriasis,
paronychia may disrupt the underlying nail matrix and sub-
sequently lead to nail plate dystrophy.
The hyponychium is the cutaneous margin underlying the
free edge of the nail plate. The nail bed ends at the hypo-
nychium. It is contiguous with the volar aspect of the
The hyponychium has a similar function as the cuticle and
acts as an adherent seal to protect the nail unit. The hypo-
nychium should not be overmanipulated during nail groom-
ing to avoid onycholysis, or separation of the nail plate from
the nail bed. This space created between the nail plate and
26. Nail physiology and grooming
Several factors affect nail growth. Nail growth peaks at
10 – 14 years and declines after 20 years. Nail growth is pro-
portional to ﬁ nger length, with fastest growth of the third
ﬁ ngernail and slowest growth of the ﬁ fth ﬁ ngernail. Nails
grow slower at night and during the winter. Other factors
causing slower nail plate growth include lactation, immobi-
lization, paralysis, poor nutrition, yellow nail syndrome,
antimitotic drugs, and acute infection. Faster nail growth has
been noted during the summer and in the dominant hand.
Pregnancy, psoriasis, and nail biting are other factors linked
to faster nail growth. Table 26.2 summarizes factors inﬂ u-
encing nail growth.
Physical p roperties of n ails
Nail c omposition
The nail plate is composed mainly of keratin, which is
embedded in a matrix of non - keratin proteins. There is wide
variation in reported percentage of inorganic elements
found in the nail plate. Several elements, including sulfur,
calcium, iron, aluminum, copper, silver, gold, titanium,
phosphorus, zinc, and sodium, are constituents of the nail
plate. Of these elements, sulfur has the greatest contribution
to nail structure and comprises approximately 5% of the nail
plate. Nail plate keratin is cross - linked by cysteine bonds,
which contain sulfur. Some studies attribute brittle nails to
decreased cysteine levels.
There is a popular misconception that calcium content is
responsible for nail hardness. This idea likely stems from
knowledge that bone density is related to calcium intake.
Calcium comprises less than 1% of the nail plate by weight.
No evidence supports that decreased calcium is linked to
brittle nails and that calcium supplementation increases nail
strength. In fact, kwashiorkor, a nutritional deﬁ ciency
caused by insufﬁ cient protein intake, is manifested by soft,
thin nails and demonstrates increased nail plate calcium.
bed retains moisture and establishes an environment for
potential pathogens, such as yeast, bacteria, or fungi.
Nail b ed
The nail bed is thin, 2 – 5 cell layer thick epithelium that
underlies the nail plate. It extends from the lunula to the
hyponychium. The nail bed is composed of longitudinal,
parallel rete ridges with a rich vascular supply which is
responsible for the pink coloration of the bed, as well as
longitudinal ridges on the ventral surface of the nail plate.
In chronic onycholysis the nail plate is separated from the
nail plate for an extended duration, the nail bed epithelium
may become keratinized, form a granular layer, and lead to
permanent onycholysis (Figure 26.4 ).
Other s tructures
The distal phalanx lies immediately beneath the nail unit.
The extensor tendon runs over the distal interphalangeal
joint and attaches to the distal phalanx 12 mm proximal to
the eponychium. Given that there is little space between the
nail unit and distal phalanx, minor injury to the nail unit
may extend to the periosteum and lead to infection.
Nail g rowth
Normal nail growth has been cited to vary from less than
1.8 mm to more than 4.5 mm per month. Average ﬁ ngernail
growth is 0.1 mm per day, or 3 mm per month. This informa-
tion is useful when determining the duration of nail pathol-
ogy. For example, if splinter hemorrhages are located 6 mm
from the proximal nail fold, it can be estimated that they
occurred from injury approximately 2 months prior. Based
on this growth rate, ﬁ ngernails grow out completely in
6 months. Toenails grow at one - third to half of the rate
of ﬁ ngernails and take 12 – 18 months to grow out
Figure 26.4 (a & b) Onycholysis.
ADORNMENT Nail Cosmetics
Table 26.2 Nail cosmetic products: ingredients and uses.
Product Ingredients Application procedures Beneﬁ ts of use Potential complications
Nail polish Film former: nitrocellulose
Plasticizer: dibutyl pthalate
Solvents and pigments
Polish is applied in several
coats with a small brush and
allowed to dry by evaporation
Provides an attractive glossy
smooth decorative surface
and camouﬂ ages nail defects
Protects nail from
dehydration and irritants
Yellow staining of nail
plate. Potential for allergy
to toluene sulfonamide
formaldehyde resin and
Nail hardener May contain formaldehyde
in a nail polish base, also
may have ﬁ bers that
reinforce the nail
Application similar to nail
polish which is applied in
Forms several layers of
protection on the nail plate
Potential allergy to
Acrylic monomer, polymer,
polymerized to form a
hard shell attached to the
nail plate or to a plastic tip
glued to the nail
Monomer (liquid) and
polymer (powder) mixed to
form a paste and polymerized
with a catalyst to a harden
Cover unsightly nail defects,
may help manage
onychotillomania and habit
Possible allergy to
acrylates, inﬂ exibility of
artiﬁ cial nail may cause
injury to nail unit
Cuticle remover Contains potassium
hydroxide or sodium
hydroxide plus humectants
Applied to cuticle for 5 – 10
minutes to soften cuticle
adhered to nail plate
Gently removes dead skin
attached to the nail plate
without mechanical trauma
Over removal of cuticle
and result in the
potential for paronychia
and secondary bacteria
and Candida infections.
Can soften the nail plate
Acetone, butyl acetate,
ethyl acetate, may also
contain moisturizer such
as lanolin or synthetic oils
Wiped across nail plate with
cotton or tissue to remove
Removes polish smoothly
without removing layers of
May dehydrate the nail
plate and periungual
Water content of the normal nail plate is reported to range
between 10% and 30%. The most commonly accepted value
is 18% water content in normal nails and 16% in brittle
nails. However, a study aimed at conﬁ rming this demon-
strated no statistically signiﬁ cant difference between normal
and brittle nails  . In addition, this study showed lower
water content than previously thought, with a mean water
content of 11.90% in normal nails and 12.48% in brittle
nails. Some limitations in this study were noted, including
analysis of only the distal nail plate. In addition, the time
between sample collection and analysis was variable, with
an average of 24 hours, and a subanalysis demonstrated loss
of water content varied signiﬁ cantly between those samples
analyzed at 1 and 24 hours.
Lipids, including squalene and cholesterol, are also con-
stituents of the nail plate and comprise 5% of the nail plate
by weight. These lipids are thought to diffuse from the nail
bed to the nail plate.
Nail ﬂ exibility
Most references to nail strength and hardness actually refer
to nail ﬂ exibility. A ﬂ exible nail will bend and conform to
physical force, whereas a hard nail will break and become
brittle. Nail ﬂ exibility is aided by plasticizers, which are
liquids that make solids more ﬂ exible. Examples of nail
plasticizers are water and lipids. Flexibility is decreased by
solvents, such as nail polish removers, which remove both
water and lipids, and detergents, which remove lipids.
Nail brittleness is caused by loss of ﬂ exibility. Brittle nails
are a common complaint and are found in 20% of the
general population and more commonly in females (Figure
26.5 ). Brittleness encompasses several nail features includ-
ing onychoschizia which is lamellar peeling of distal nail
plate (Figure 26.6 ), splitting and notching sometimes associ-
ated with ridges, and fragility of the distal nail plate, lamellar
splitting of the free end of the nail plate. Several attempts
have been made to deﬁ ne brittleness with objective meas-
urements, including Knoop hardness, which evaluates
indentation at a ﬁ xed weight; modulus of elasticity, which
describes the relationship between force/area and deforma-
tion produced; tensile strength; and a brittleness grading
Although there are systemic and cutaneous conditions
that may cause brittle nails, exogeneous causes are more
26. Nail physiology and grooming
Figure 26.5 (a – c) Brittle nails.
Figure 26.6 Onychoschizia, distal lamallar peeling of the nail plate.
ADORNMENT Nail Cosmetics
Manicure and pedicures are the process of grooming the
ﬁ ngernails and toenails respectively at home or in a nail
salon (Figure 26.7 ). The procedure involves soaking the
nails to soften prior to trimming and shaping the nail plate.
Excess cuticle is removed from the nail plate using a chemi-
cal cuticle remover and often a metal implement. The nails
are then ﬁ nished with a shiny, smooth coat of nail enamel,
commonly called nail polish, sandwiched between a base
coat and top coat, or the nails may be buffed to a soft luster.
Other procedures such as acrylic gel or silk wrap enhance-
ments may be added to the basic manicure. These nail
extension procedures involve applying product to the
natural nail or to a plastic tip glued to the nail. The material
are applied and shaped before curing or polymerizing to
form a hard surface.
Nail t rimming
Most nail experts advocate shaping nails with an emery
board rather than clipping or cutting nails. Filing should be
common. These include mechanical trauma, exposure to
solvents and extraction of plasticizers, and repeated hydra-
tion and drying of nails.
Nail t hickness
Thickness of the nail plate is determined primarily by matrix
length and rate of growth. Measurements of distal plate
thickness demonstrate greatest thickness in the thumbnail,
followed by the second, third, fourth, and ﬁ fth ﬁ ngernails.
Thickness also is inﬂ uenced by sex, with males having an
average nail plate thickness of 0.6 mm, compared to 0.5 mm
Nail g rooming p rinciples
Nail c are
Several principles of nail care should be observed during nail
grooming to maintain normal nail structure.
Figure 26.7 (a) Manicure; (b – d) Pedicure.
26. Nail physiology and grooming
important to be aware of possible adverse effects related to
procedures or to materials used in nail cosmetics (Figure
Allergic r eactions to n ail c osmetic i ngredients
The most common allergen in nail polish is toluene sulfona-
mide formaldehyde resin with sensitization occurring in
up to 3% of the population. Other potential allergens are
cyanoacrylate nail glue, formaldehyde in nail hardeners, and
ethylmethacrylate in sculptured nails. Allergic contact der-
matitis from nail cosmetics is seen on periungual skin, as
well as the eyelids, face, and neck, caused by touching these
areas with freshly polished ﬁ ngernails (Figure 26.11 ).
Irritant r eactions
Common nail products that cause irritant reactions include
acetone or acetate nail polish removers and cuticle removers
carried out with the ﬁ le exactly perpendicular to the nail
surface to avoid inducing onycholysis. Proper ﬁ ling of the
free edge of nail plate reduces sharp edges that may catch
and cause nail plate tearing. If nails must be clipped or cut,
this should be performed after they have been hydrated
which maximizes nail ﬂ exibility and prevents breakage
during trimming. Nails should also be kept as short as pos-
sible. Long nails, especially those that are brittle, may act as
a lever and create onycholysis.
Nail b ufﬁ ng and ﬁ ling
The dorsal nail plate surface is often ﬁ led to remove shine
from the natural nail plate at nail salons prior to application
of nail products or artiﬁ cial nails. Care must be taken to
avoid excessive ﬁ ling, especially with electric drills. The nail
plate is approximately 100 cell layers thick. If ﬁ ling must be
done, only 5% of the nail plate thickness, or approximately
ﬁ ve cell layers, should be removed which is just enough to
remove the shine of the dorsal nail plate in order to facilitate
adherence of the product to the nail plate. Limited bufﬁ ng
to reduce nail ridging is acceptable, but excessive bufﬁ ng
thins the nail plate and should be avoided.
Care for b rittle n ails
Brittle nails should be treated by avoiding nail trauma and
increasing ﬂ exibility. Nails should be kept short. This pre-
vents lifting of the nail plate, disruption of the hypony-
chium, and onycholysis. In addition, nails should be trimmed
after they have been hydrated and are the most ﬂ exible.
Moisturizing the nail plate increases ﬂ exibility and helps
avoid brittle nails. Some experts recommend moisturizing
up to four times daily. Avoiding solvents and frequent
hydration and dessication of nails also helps maintain ﬂ ex-
ibility. There is controversy regarding avoidance of nail cos-
metics in the management of brittle nails. Some believe that
nail polish is protective and seals the moisture in the nail
plate by preventing rapid evaporation. Nail polish also pro-
tects the nail plate from some environmental irritants. There
is some concern that overuse of nail polish remover will
dehydrate the nail and exacerbate brittleness.
Biotin has also been advocated for brittle nails, but results
are inconclusive. The recommended dose is 2.5 – 5 mg/day,
which is 100 – 200 times the recommended daily allowance.
Given that biotin has relatively few side effects, most experts
recommend its use, in addition to the above grooming
Adverse e ffects from n ail g rooming
Nail cosmetics are safely used by millions of people world-
wide. In addition to enhancing the appearance of normal
nails, cosmetics are useful for improving the appearance of
unsightly nail dystrophy caused by medical disease, such as
psoriasis (Figure 26.8 ), onychomycosis (Figure 26.9 ), or
trauma. Although nail cosmetics rarely cause problems, it is
Figure 26.8 Psoriasis: salmon patch oil drop discoloration.
Figure 26.9 Onychomycosis.
ADORNMENT Nail Cosmetics
Figure 26.10 Yellow staining from nail polish.
Figure 26.11 Allergic contact dermatitis from nail cosmetics. (a) On the eyelid. (b) On periungal skin caused by acrylates.
Figure 26.12 (a & b) Keratin granulations.
with sodium hydroxide. Reactions are manifested as an irri-
tant dermatitis of the periungual skin and as brittle nails,
including onychoschizia. Prolonged use of nail polish induce
keratin granulations on the nail plate. This commonly is
seen when fresh coats of nail enamel are applied on top of
old enamel for several weeks. These granulations cause
superﬁ cial friability of the nail plate (Figure 26.12 ).
Nail c osmetic p rocedures
Several nail problems, including paronychia, onycholysis,
and thinning of the nail plate, may be mechanically induced
by cosmetic procedures. Paronychia, or inﬂ ammation of
the proximal nail fold, is often caused by cutting or pushing
back the cuticle, leading to separation of the proximal
nail fold and the nail plate. Sharp manicure instruments
used to clean under the nail plate may induce onycholysis
and create an environment for secondary bacterial and
26. Nail physiology and grooming
fungal infection. Onycholysis may be exacerbated by long
artiﬁ cial nails because of increased mechanical leverage.
Nail drills or excessive ﬁ ling and bufﬁ ng may lead to
thinning of the nail plate and brittle nails. Breaks in the
integrity of the nail unit allow access of microorganisms
such as Candida and Pseudomonas (Figure 26.13 ) and result
in exacerbation of paronychia and onycholysis. Some basic
principles for safe use of nail cosmetics are outlined in
Table 26.3 .
Nail cosmetics is a multibillion dollar industry which con-
tinues to grow. Thorough knowledge of nail anatomy and
physiology is essential for the safe use and development of
Figure 26.13 Infection caused by Pseudomonas .
Table 26.3 Information for patients for safe nail cosmetic use. After
Rich  .
• Be sure that the salon sterilizes instruments, preferably with an
autoclave. Some salons offer instruments for clients to purchase
• Stinging, burning, or itching following a nail salon treatment may
be signs of an allergic reaction to a cosmetic ingredient. Remove
the product and seek medical evaluation by a dermatologist
• If using artiﬁ cial nail extensions, keep them short. Long nails can
cause mechanical damage to the nail bed. Remove extensions at
the ﬁ rst sign of onycholysis and avoid enhancements until the nail
• Do not allow nail technician to cut or clip cuticles. Cuticles serve an
important function and should not be cut. They may be pushed
back gently with a soft towel after soaking the nails or bathing
1 Stern DK , et al . ( 2007 ) Water content and other aspects of brittle
versus normal ﬁ ngernails . J Am Acad Dermatol 57 , 31 – 36 .
2 Rich P . ( 2001 ) Nail cosmetics and camouﬂ aging techniques .
Dermatol Ther 14 , 228 – 36 .
Further r eading
Chang RM , Hare AQ , Rich P . ( 2007 ) Treating cosmetically induced
nail problems . Dermatol Ther 20 , 54 – 9 .
Baran R , Dawber RPR , de Berker DAR , Haneke E , Tosti A . ( 2001 )
Diseases of the Nails and their Management , 3rd edn. Malden, MA :
Blackwell Science .
DeGroot , AC , Weyland JW . ( 1994 ) Nail cosmetics . In: Unwanted
Effects of Cosmetics and Drugs used in Dermatology , 3rd edn. New
York, Oxford : Elsevier , 524 – 9 .
Draelos Z . ( 2000 ) Nail cosmetic issues . Dermatol Clin 18 , 675 – 83 .
Iorizzo M , Piraccini B , Tosti , A . ( 2007 ) Nail cosmetics in nail disor-
ders . J Cosmet Dermatol 6 , 53 – 6 .
Paus R , Peker S , Sundberg JP . ( 2008 ) Biology of hair and nails . In:
Bolognia JL , Jorizzo JL , Rapini RP , eds. Dermatology , 2nd edn.
Elsevier , pp. 965 – 86 .
Rich P . ( 2008 ) Nail surgery . In: Bolognia JL , Jorizzo JL , Rapini RP ,
, 2nd edn. Elsevier , pp. 2259 – 68 .
Schoon DD . ( 2005 ) Nail Structure and Product Chemistry , 2nd edn.
Thompson Corporation .
Scher RK , Daniel CR . ( 2005 ) Nails: Diagnosis, Therapy, Surgery , 3rd
edn. Elsevier .